added coffeelint support closes #118

I wanted to get notifications on improper formatting, so (after looking at #118) I added support for coffeelint to the coffeescript linter. It checks to see if coffeelint is installed, and uses it only if it is. Otherwise, it falls back to just using `coffeescript -l`. I haven't tested this on windows (but it _should_ probably work - it doesn't rely on any Unix-only features)... so somebody who uses windows should test this out. I have tested it on Ubuntu, but not extensively.

FYI: `coffeelint` also checks for syntax errors like `coffeescript -l` does (I assume it just passes the code through `coffeescript -l` and returns that in addition to it's own output). So using coffeelint is really just an enhancement, and shouldn't require a option to use one linter or the other since it automatically uses the best available one & if users don't like coffeelint's linting (but still have it installed for whatever reason), they can disable all the extra features of coffeelint through the coffeelint configuration in ST2.