Revert "Upgrade RuboCop to 0.23.0"

This reverts commit 1e3e4200579fd567a53b417f15776c98d1e2650d.

Rubocop has changed their configuration structure which will break existing
config for all of our users. Until we find a strategy to deal with this, we
should not upgrade any higher.
Lock RuboCop to v0.22.0

* Update configuration link to point to the right tag of RuboCop
Update configuration.haml

That ain't YAML. This is YAML.
Extract CommentingPolicy policy object

* Extract `CommentingPolicy` object for logic around permitting
  Hound to comment on a line in a pull request
Add Hound logo to home page

* Add Hound SVGs to home page
* Move line on homepage to the left
* Remove old hound image

https://trello.com/c/U2GJGKlo
Merge pull request #286 from bhardin/patch-1

Update configuration.haml
Clean up Commenter and CommentingPolicy specs

* Remove specs testing logic currently tested in `CommentingPolicy`
  specs from `Commenter`
* Don't stub unused and nonexistent methods in `CommentingPolicy` specs
Rename CommentingPolicy spec to have suffix

Tighten up some lines that dont need to wrap beyond one line.
Use CoffeeLint to catch line length violations
Allow CoffeeLint configuration to be overridden
Check additional rules regarding CoffeeScript

* Delete trailing whitespace.
* Use 2 space indentation (no tabs).
* Use PascalCase for classes.

Add remaining rules to default CoffeeLint config for completeness.
Style fixes
Replace fetch with square brackets element reference
Construct *StyleGuide objects using meta-programming
Update names of custom config files

Make `.hound` a common prefix and add the language name before the file
extension. This is a step towards making the names of the config files stable
while the underlying tool might change.
Add info about custom CoffeeScript config to view
Default override_config_content to '{}' instead of nil

An explicit `nil` might still be passed as a parameter, so add the fallback to
the line with the ivar assignment.
Undo config file rename and addition

There is still an active discussion on how best to handle custom configuration,
so leave the current config override file as-is and avoid adding a second config
file. Update tests and the view accordingly.