Multi-threaded coffee-script compilation

We hit a bottleneck in coffee-mil : coffee-script compilation with large amount of coffee -script sources.

We write our Web App majoritly as coffee-script. Thus, a full web app can take up to 1 minute to compile. 

This PR is a proposal for multi-threaded coffee-script compilation. This is not, in any way, a PR to be merged.

I see 2 points to by-pass this bottleneck : 
* optimize Rhino CoffeeScript compilation
* Multi-thread CoffeeScript compilation

This PR is a proposal for the second point (multi-thread). It's just an example reducing my test sample (from 55 to 43 seconds compilation).

Linking this with a Rhino optimisation we could gain create productivity over CoffeeScript compilation. For now, I've not yet investigated how to optimize Rhino coffee-script compilation.

Furthermore, this multi-thread implementation is very basic, I'm not a specialist in multi-thread implementation.

To launch this sample : 
mvn clean install -DthreadedCompile=true -DmaxThread=5

maxThread can be set to any values(default 4).

This PR is up to discussions.

PS : I can't share my test sample right now. Updating as soon as I have approval.

commit comment : 
Add a new CoffeeScriptProcessor with multi-thread capability

Signed-off-by: nicolas-rempulski <nicolas.rempulski@gmail.com>