Add ExtraSpacing cop that detects unnecessary whitespace.
Merge pull request #1475 from blainesch/feature/spacing

Add ExtraSpacing cop that detects unnecessary whitespace.
Support style-guide only usage

Many cops that have been implemented and enabled by default have no
correlation to a style-guide rule: `Metrics/ClassLength`,
`Metrics/AbcSize`, `Metrics/PerceivedComplexity` just to name a few. In
cases where these cops find violations, there's little recourse as the
rules cannot be traced back to a meaningful discussion or consensus.

The `--only-guide-cops` and `AllCops/StyleGuideCopsOnly` options give
users an easy method of invoking RuboCop in a way that's more congruent
with the rules of the style guide.

Working around `GuardClause` violation in `Runner#filter_cop_classes`.
Merge pull request #1454 from marxarelli/feature/only-guide-cops

Support style-guide only usage
[Fix #1325] Don't consider corrected offenses as failure

Disregard corrected offenses when determining the exit code of
the program.
Merge pull request #1479 from jonas054/1325_exit_code

[Fix #1325] Don't consider corrected offenses as failure