Completely reorganized file cache - no supports only immutable files with any custom meta data.
Persistence supported by transactions journal that guaranties atomic records.
Meta-data serialized through the Kryo framework.
Implemented completely sync and partially async versions of cache.
TODO:
 - improve test coverage (including stress-tests), maybe some refactoring
 - implement some basic logging for IO-fails
 - javadoc
 - readme
 - think about file and meta consistency - there is rare case when they don't