Update `line_number` to `patch_position` where it makes sense.
Update readme for development installation.
Document testing enviroment setup
Update style guide link in README
Add config option to display cop names in comments

* add `ShowCopNames` config option to show cop names in GitHub comments
  * turned off by default
  * to enable set `ShowCopNames: true` in `.hound.yml`
Fix erroneous logic to disallow duplicate comments

* This commit fixes two logic errors in be2dd34178
* In `Commenter#previous_line_comments`, compare position of existing
  comment to line patch position rather than line number
* In `CommentPolicy#violation_not_previously_reported?`, compare new
  violation message to body content of existing comments rather than the comment
  objects
* https://trello.com/c/ha2hgFj2/283-avoid-commenting-a-second-time-after-a-force-push