model caching

Adds basic model caching functionality to active record. To enable caching for a particular model, set a static variable called "cache" to true in your model subclass, and configure a cache adapter. Set a static variable called "cache_expire" to a value in seconds; otherwise your Cache configuration expire period will be used.

Thanks for the quick fix, guys, sorry 'bout that. I was always vaguely disturbed by the idea of a public static in Cache depending on 'initialize' being fired to be valid. What do you think about the idea of initializing it at declaration, instead?