Implementing increment/decrement for file cache adapter.
Refactoring file cache adapter; improve parser.
Cache file adapter incr/decr to not alter expiry.
Adding tests for incr/decr of file cache adapter.
Require increment/decrement methods for cache adapters.
Correcting documented cache incr/decr return and formatting.
Adding note about on-the-fly invalidation.
Merge pull request #1084 from davidpersson/cache-incr-decr

Make Cache increment/decrement methods available in every adapter