Nothing ground-breaking this time around, but the release is pretty exciting non-the-less.
It packs a whole new category of cops (`Performance`) and a bunch of new Rails cops.
A lot of the existing cops got new customization options and we squashed a ton of bugs.

Thanks to everyone who contributed to this release!

### New features

* [#1600](https://github.com/rubocop/rubocop/issues/1600): Add `line_count_based` and `semantic` styles to the `BlockDelimiters` (formerly `Blocks`) cop. ([@clowder][], [@mudge][])
* [#1712](https://github.com/rubocop/rubocop/pull/1712): Set `Offense#corrected?` to `true`, `false`, or `nil` when it was, wasn't, or can't be auto-corrected, respectively. ([@vassilevsky][])
* [#1669](https://github.com/rubocop/rubocop/pull/1669): Add command-line switch `--display-style-guide`. ([@marxarelli][])
* [#1405](https://github.com/rubocop/rubocop/issues/1405): Add Rails TimeZone and Date cops. ([@palkan][])
* [#1641](https://github.com/rubocop/rubocop/pull/1641): Add ruby19_no_mixed_keys style to `HashStyle` cop. ([@iainbeeston][])
* [#1604](https://github.com/rubocop/rubocop/issues/1604): Add `IgnoreClassMethods` option to `TrivialAccessors` cop. ([@bbatsov][])
* [#1651](https://github.com/rubocop/rubocop/issues/1651): The `Style/SpaceAroundOperators` cop now also detects extra spaces around operators. A list of operators that *may* be surrounded by multiple spaces is configurable. ([@bquorning][])
* Add auto-correct to `Encoding` cop. ([@rrosenblum][])
* [#1621](https://github.com/rubocop/rubocop/issues/1621): `TrailingComma` has a new style `consistent_comma`. ([@tamird][])
* [#1611](https://github.com/rubocop/rubocop/issues/1611): Add `empty`, `nil`, and `both` `SupportedStyles` to `EmptyElse` cop. Default is `both`. ([@rrosenblum][])
* [#1611](https://github.com/rubocop/rubocop/issues/1611): Add new `MissingElse` cop. Default is to have this cop be disabled. ([@rrosenblum][])
* [#1602](https://github.com/rubocop/rubocop/issues/1602): Add support for `# :nodoc` in `Documentation`. ([@lumeet][])
* [#1437](https://github.com/rubocop/rubocop/issues/1437): Modify `HashSyntax` cop to allow the use of hash rockets for hashes that have symbol values when using ruby19 syntax. ([@rrosenblum][])
* New cop `Style/SymbolLiteral` makes sure you're not using the string within symbol syntax unless it's needed. ([@bbatsov][])
* [#1657](https://github.com/rubocop/rubocop/issues/1657): Autocorrect can be turned off on a specific cop via the configuration. ([@jdoconnor][])
* New cop `Style/AutoResourceCleanup` suggests the use of block taking versions of methods that do resource cleanup. ([@bbatsov][])
* [#1275](https://github.com/rubocop/rubocop/issues/1275): `WhileUntilModifier` cop does auto-correction. ([@lumeet][])
* New cop `Performance/ReverseEach` to convert `reverse.each` to `reverse_each`. ([@rrosenblum][])
* [#1281](https://github.com/rubocop/rubocop/issues/1281): `IfUnlessModifier` cop does auto-correction. ([@lumeet][])
* New cop `Performance/Detect` to detect usage of `select.first`, `select.last`, `find_all.first`, and `find_all.last` and convert them to use `detect` instead. ([@palkan][], [@rrosenblum][])
* [#1728](https://github.com/rubocop/rubocop/pull/1728): New cop `NonLocalExitFromIterator` checks for misused `return` in block. ([@ypresto][])
* New cop `Performance/Size` to convert calls to `count` on `Array` and `Hash` to `size`. ([@rrosenblum][])
* New cop `Performance/Sample` to convert usages of `shuffle.first`, `shuffle.last`, and `shuffle[Integer]` to `sample`. ([@rrosenblum][])
* New cop `Performance/FlatMap` to convert `Enumerable#map...Array#flatten` and `Enumerable#collect...Array#flatten` to `Enumerable#flat_map`. ([@rrosenblum][])
* [#1144](https://github.com/rubocop/rubocop/issues/1144): New cop `ClosingParenthesisIndentation` checks the indentation of hanging closing parentheses. ([@jonas054][])
* New Rails cop `FindBy` identifies usages of `where.first` and `where.take`. ([@bbatsov][])
* New Rails cop `FindEach` identifies usages of `all.each`. ([@bbatsov][])
* [#1342](https://github.com/rubocop/rubocop/issues/1342): `IndentationConsistency` is now configurable with the styles `normal` and `rails`. ([@jonas054][])

### Bugs fixed

* [#1705](https://github.com/rubocop/rubocop/issues/1705): Fix crash when reporting offenses of `MissingElse` cop. ([@gerry3][])
* [#1659](https://github.com/rubocop/rubocop/pull/1659): Fix stack overflow with JRuby and Windows 8, during initial config validation. ([@pimterry][])
* [#1694](https://github.com/rubocop/rubocop/issues/1694): Ignore methods with a `blockarg` in `TrivialAccessors`. ([@bbatsov][])
* [#1617](https://github.com/rubocop/rubocop/issues/1617): Always read the html output template using utf-8. ([@bbatsov][])
* [#1684](https://github.com/rubocop/rubocop/issues/1684): Ignore symbol keys like `:"string"` in `HashSyntax`. ([@bbatsov][])
* Handle explicit `begin` blocks in `Lint/Void`. ([@bbatsov][])
* Handle symbols in `Lint/Void`. ([@bbatsov][])
* [#1695](https://github.com/rubocop/rubocop/pull/1695): Fix bug with `--auto-gen-config` and `SpaceInsideBlockBraces`. ([@meganemura][])
* Correct issues with whitespace around multi-line lambda arguments. ([@zvkemp][])
* [#1579](https://github.com/rubocop/rubocop/issues/1579): Fix handling of similar-looking blocks in `BlockAlignment`. ([@lumeet][])
* [#1676](https://github.com/rubocop/rubocop/pull/1676): Fix auto-correct in `Lambda` when a new multi-line lambda is used as an argument. ([@lumeet][])
* [#1656](https://github.com/rubocop/rubocop/issues/1656): Fix bug that would include hidden directories implicitly. ([@jonas054][])
* [#1728](https://github.com/rubocop/rubocop/pull/1728): Fix bug in `LiteralInInterpolation` and `AssignmentInCondition`. ([@ypresto][])
* [#1735](https://github.com/rubocop/rubocop/issues/1735): Handle trailing space in `LineEndConcatenation` autocorrect. ([@jonas054][])
* [#1750](https://github.com/rubocop/rubocop/issues/1750): Escape offending code lines output by the HTML formatter in case they contain markup. ([@jonas054][])
* [#1541](https://github.com/rubocop/rubocop/issues/1541): No inspection of text that follows `__END__`. ([@jonas054][])
* Fix comment detection in `Style/Documentation`. ([@lumeet][])
* [#1637](https://github.com/rubocop/rubocop/issues/1637): Fix handling of `binding` calls in `UnusedBlockArgument` and `UnusedMethodArgument`. ([@lumeet][])

### Changes

* [#1397](https://github.com/rubocop/rubocop/issues/1397): `UnneededPercentX` renamed to `CommandLiteral`. The cop can be configured to enforce using either `%x` or backticks around command literals, or using `%x` around multi-line commands and backticks around single-line commands. The cop ignores heredoc commands. ([@bquorning][])
* [#1020](https://github.com/rubocop/rubocop/issues/1020): Removed the `MaxSlashes` configuration option for `RegexpLiteral`. Instead, the cop can be configured to enforce using either `%r` or slashes around regular expressions, or using `%r` around multi-line regexes and slashes around single-line regexes. ([@bquorning][])
* [#1734](https://github.com/rubocop/rubocop/issues/1734): The default exclusion of hidden directories has been optimized for speed. ([@jonas054][])
* [#1673](https://github.com/rubocop/rubocop/issues/1673): `Style/TrivialAccessors` now requires matching names by default. ([@bbatsov][])

[@bbatsov]: https://github.com/bbatsov
[@jonas054]: https://github.com/jonas054
[@yujinakayama]: https://github.com/yujinakayama
[@dblock]: https://github.com/dblock
[@nevir]: https://github.com/nevir
[@daviddavis]: https://github.com/daviddavis
[@sds]: https://github.com/sds
[@fancyremarker]: https://github.com/fancyremarker
[@sinisterchipmunk]: https://github.com/sinisterchipmunk
[@vonTronje]: https://github.com/vonTronje
[@agrimm]: https://github.com/agrimm
[@pmenglund]: https://github.com/pmenglund
[@chulkilee]: https://github.com/chulkilee
[@codez]: https://github.com/codez
[@emou]: https://github.com/emou
[@skanev]: http://github.com/skanev
[@claco]: http://github.com/claco
[@rifraf]: http://github.com/rifraf
[@scottmatthewman]: https://github.com/scottmatthewman
[@ma2gedev]: http://github.com/ma2gedev
[@jeremyolliver]: https://github.com/jeremyolliver
[@hannestyden]: https://github.com/hannestyden
[@geniou]: https://github.com/geniou
[@jkogara]: https://github.com/jkogara
[@tmorris-fiksu]: https://github.com/tmorris-fiksu
[@mockdeep]: https://github.com/mockdeep
[@hiroponz]: https://github.com/hiroponz
[@tamird]: https://github.com/tamird
[@fshowalter]: https://github.com/fshowalter
[@cschramm]: https://github.com/cschramm
[@bquorning]: https://github.com/bquorning
[@bcobb]: https://github.com/bcobb
[@irrationalfab]: https://github.com/irrationalfab
[@tommeier]: https://github.com/tommeier
[@sfeldon]: https://github.com/sfeldon
[@biinari]: https://github.com/biinari
[@barunio]: https://github.com/barunio
[@molawson]: https://github.com/molawson
[@wndhydrnt]: https://github.com/wndhydrnt
[@ggilder]: https://github.com/ggilder
[@salbertson]: https://github.com/salbertson
[@camilleldn]: https://github.com/camilleldn
[@mcls]: https://github.com/mcls
[@yous]: https://github.com/yous
[@vrthra]: https://github.com/vrthra
[@SkuliOskarsson]: https://github.com/SkuliOskarsson
[@jspanjers]: https://github.com/jspanjers
[@sch1zo]: https://github.com/sch1zo
[@smangelsdorf]: https://github.com/smangelsdorf
[@mvz]: https://github.com/mvz
[@jfelchner]: https://github.com/jfelchner
[@janraasch]: https://github.com/janraasch
[@jcarbo]: https://github.com/jcarbo
[@oneamtu]: https://github.com/oneamtu
[@toy]: https://github.com/toy
[@Koronen]: https://github.com/Koronen
[@blainesch]: https://github.com/blainesch
[@marxarelli]: https://github.com/marxarelli
[@katieschilling]: https://github.com/katieschilling
[@kakutani]: https://github.com/kakutani
[@rrosenblum]: https://github.com/rrosenblum
[@mattjmcnaughton]: https://github.com/mattjmcnaughton
[@huerlisi]: https://github.com/huerlisi
[@volkert]: https://github.com/volkert
[@lumeet]: https://github.com/lumeet
[@mmozuras]: https://github.com/mmozuras
[@d4rk5eed]: https://github.com/d4rk5eed
[@cshaffer]: https://github.com/cshaffer
[@eitoball]: https://github.com/eitoball
[@iainbeeston]: https://github.com/iainbeeston
[@pimterry]: https://github.com/pimterry
[@palkan]: https://github.com/palkan
[@jdoconnor]: https://github.com/jdoconnor
[@meganemura]: https://github.com/meganemura
[@zvkemp]: https://github.com/zvkemp
[@vassilevsky]: https://github.com/vassilevsky
[@gerry3]: https://github.com/gerry3
[@ypresto]: https://github.com/ypresto
[@clowder]: https://github.com/clowder
[@mudge]: https://github.com/mudge
