Juggernaut v2.0 alpha

* Implements PHP-FIG cache proposal #4 (https://github.com/Crell/fig-standards/tree/Cache)
* Multiple *new* adapters:
    * APC
    * Memcached
    * Memory (Array)
    * MySQLi
    * PDO
* A new `Chained` adapter which takes multiple adapters and manages cache across all of them. This allows you to hit a fast local memory cache before a slower remote database cache.
* Adds individual cache item expiration
* Adds individual cache item invalidation

WIP: do not merge yet.