Update rubocop and dependant gems

houndci.com was giving me false warnings about things the latest
Rubocop gem doesn’t complain about.
Merge pull request #273 from blacklane/update-rubocop-gem-0.22.0

Upgrade RuboCop to version 0.22.0.
Assign filename to buffer name

* This should help us exclude files using RuboCop
Upgrade RuboCop to 0.23.0

* Change Rubocop reference to RuboCop
* Prefix configuration according to new syntax
Use Linguist to determine file language

Using Linguist should allow us to lint Ruby source files not necessarily ending
in `.rb`, such as `Gemfile`, `Rakefile`, `config.ru` etc. Leveraging Linguist
should also make it easier to extend Hound with support for additional
languages, since we don't have to concern ourselves with the mechanics of
finding out what files belong to that language.

Also install `libicu-dev` on Tracis CI in order for `charlock_holmes` (a
dependency of Linguist) to install properly.
Merge pull request #275 from Koronen/vk-linguist

Use Linguist to determine file language
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