Rename brunchcoffee to brunch.coffee

so that coffee-script's node monkey-patches take effect, particularly
for child_process.fork

https://github.com/jashkenas/coffee-script/blob/84b8b5cceef6c452996d022c4c2d47dc8c8a5ccc/src/coffee-script.coffee#L182-L192
Initial basic worker structure
Worker compilation proof of concept
Refactor worker code to be totally unobtrusive
Filter worker plugins to only compilers and linters
Complete workers implementation
Better workers settings
Workers docs
Merge pull request #687 from brunch/topics/workers

Workers