Added support for @ClassName style class declarations

Fixes issue https://github.com/lukaszkorecki/CoffeeTags/issues/17

I've just started trying out CoffeeTags, and I find the @ClassName style of exports fairly useful. I can see at least one other person would find this useful.  So I've written a simple patch, I've added support with a passing test.

The patch should apply cleanly to the the current master (b1d5763).