Added support for letting user configure cache component
Removed $this->lifetime parameter to $this->cache()

Wasn't needed, we were accessing $this->lifetime directly inside cache() anyway.
Fixed calls to unknown set().

Actual method was called cache(). Woes of editing files directly on github, don't get to know non-existent functions.
Merge pull request #2 from shoaibi/patch-1

Added support for letting user configure cache component