New Features
* Add `SpaceAfterComment` which checks for spacing after comment literal
Changes
* Drop support for Ruby 1.9.3
* `Shorthand` linter will now forbid the use of shorthand properties if
`allowed_shorthands` option is set to an empty list
* Change Rake task to respect `scss_files` option if no explicit files are
specified
Bug Fixes
* Fix `scss_files` option to accept an array of patterns
* Fix `--exclude-linter` flag
* Fix `ColorKeyword` linter to allow color keywords to be used as arguments
in `map-*`-related function calls
* Fix `SpaceAfterComma` linter to report correct column number
* Fix `PrivateNamingConvention` to consider functions/mixins used inside other
functions/mixins
* Fix `Shorthand` to not report shorthanded values with `!important` as having
a shorthand length not specified in `allowed_shorthands`
* Fix `UnnecessaryMantissa` to ignore decimal values in URL literals
* Fix `PlaceholderInExtend` to report comma sequences starting with a
placeholder
* Fix `StringQuotes` linter to ignore `@charset` directives since they must
[_always_ use double quotes](https://www.w3.org/TR/css-syntax-3/#charset-rule)