Adds Syntastic checker.

* Initial version of the Syntastic syntax checker with SyntaxError & ParseError errorformats

Hey Luke,

Finally got around to this. I'm not using Riml for this because Syntastic makes use of mixins in a form that I'm not sure how to translate to.

One feature that I'd like is, for the `signs` window to show the cursor at the line number with the error. And additionally when you are in the line, the status line to update with the error on that line. 

This works in most languages but I have no idea how it's implemented. The Ruby one is even more advanced in that it also highlights things like `unused variables`. Currently the `:Errors` window does show the errors found via `riml -k`, just don't how how to integrate this with the `signs` and `statusline`.

But it's a start. :)