Add function and method definition syntax highlighting

[zeekay]

This adds coffeeFunction and coffeeMethod syntax elements which are linked to
coffeeStatement and coffeeObjAssign, respectively. This ensures that existing
themes will continue to behave as they have, but makes it possible to highlight
functions and methods separately à la Sublime Text. For instance one might want to use their theme's function and method highlight colors:

hi link coffeeFunction Function
hi link coffeeMethod Method

Syntax highlighting similar to Sublime Text is achievable with the following:

hi link coffeeFunction Function
hi link coffeeMethod Function
hi link coffeeObjAssign Statement

Based on the efforts of @seanhess, and addressing the issue raised by @bergman with #102 (function calls incorrectly being captured).

[brentropy]

What is the status of this? I was considering doing a similar pull request until I found this one.

[pmaoui]

I'm also waiting for this one !