Allow setting options after compiler is constructed

[robfig]

Just adding a setOptions() method.

This is desirable because individual snippets of coffee may have different preferences on whether they want to be compiled with 'bare' or not. Additionally, creating a new instance of the compiler every time seems wasteful given the relatively complicated constructor.

FYI, I'm using JCoffeeScript in https://github.com/robfig/play-coffee

Thanks! -Rob