Using YUI compressor to compress all files in one shot rather than spawing a JVM per file.

By compressing all files in a given directory in shot, we can save the time it takes for the task to perform a JVM lifecycle operation per file YUI tries to compress.
PENDING: I've not moved the css_sass directory compression to this new style yet.
Moving css_sass directory compression to the new way.

Implemented the pending section of the last commit (758610379f7cacd6be1584447d9acebc7e0aa209). Compression and merging happens in two separate flows rather than together.
Merge branch 'master' into faster-compression
Merge pull request #272 from sachinsudheendra/faster-compression

Using YUI compressor to compress all files in one shot rather than spawing a JVM per file.