Faster page loads when adding page to cache; do async opp.

Probably won't work with xml & json... need to think of how to do this.

Need to allow async php to be an option. default would be enabled.

Also while here, make it so one can cache just css/js, no html. Will allow for higher boost adoption rates and fix some annoying bugs, and potentially obsolete the css gzip module; or at least allow this to do things that module cant do (gzip non aggregated files).

Refactored some code as well.

committed