Add coffeelint to check for style guide violations

[mrmr1993]

This PR attempts to add automatic style guide checking. Specifically, it

• moves the style guide into the repository.
• adds a coffeelint configuration to check (a subset of) the style guide recommendations.
• adds cake lint to run coffeelint.
• integrates cake lint into travis-ci.
• makes the changes suggested by cake lint.

All code style violations caught by coffeelint are currently set to warn, so will not fail the travis build. This can be changed if certain violations are deemed unacceptable.

[deiga]

You should actually rewrite this method to use bindings correctly:

 should "handle self-removing handlers correctly", ->
     @handlerStack.push { keydown: => @handler1Called = true }
     @handlerStack.push { keydown: =>
       @handler2Called = true
...

[mrmr1993]

@deiga done

[mrmr1993]

Just realised that the whole point of the test is that @remove() removes the handler, and so we need the ctx variable. Reverted.