Refactored `Cache::increment()`.
Renamed `Cache::hasTag()` -> `Cache::existsTag()`.
Renamed `Cache::has()` -> `Cache::exists()`.
Fixed PHPDoc.
Implemented CacheStub.
Skipped `MemcacgedTest::testStatus()`.
Removed `Cache::$enabled`.
Changed cache: `CacheFile` -> `CacheStub`.
Fixed main config.