Added auto correct with -a flag

[nicollis]

added the ability to use rubocop's -a flag and only autocorrect the code that git diff views as added.

it does this by first mapping out the changed lines by some small edits to the patch.rb file

it then takes that those line numbers and adds rubocop en/disable comments to the files around the edited code disabling all other code from being processed by rubocop, while adding lines it maps out what lines its editing

after rubocop runs its validations we then go back though using the edited lines map we remove the added comments. We do this to avoid removing rubocop comments that might already exist in the project

[dhempy]

Yes, please, @m4i !

[jmondo]

yes plz

[peterwilson]

Are there plans to add this to the main repo's master branch?

[dnamsons]

/cc @m4i