Implemented basic disk caching of compiled scss

Signed-off-by: Peter Jacobs <auchwertin@gmail.com>
Removed unneeded parameter, now uses cache in directory $opts['diskcache'] if diskcache is set.
Also some minor cleanup of indentation and code style
Some additional cleanup, clarified diskcache comments somewhat
Merge pull request #1 from Crespyl/master

Implemented basic disk caching of compiled scss