Issue #45:
 - Adapted `Store` SPI to current `Cache` API
 - `Ehcache` delegates to `Store` and handles `CacheAccessExceptions`
Issue #45:
 - Moved all methods that weren't doing anything other than throwing to `Ehcache`
Issue #45:
 - Deleted SerializingCache
 - Renamed HeapResource to EhcacheProvider
Issue #45:
 - Wired Store stuff in, single provider: OnHeapStore
Issue #45:
 - Clean ups, leaving HeapCache et al for now, for illustration purposes
#32 Add programatic API for cache capacity control
#32 add xml configuration for cache capacity constraints