* Added TabletLevelDB::GenerateRawValue() and DivideRawValue().
* Added TabletHashKey class.
* Renamed TabletKeyRange class into TabletHashKeyRange.
* Disabled the test codes because the range keys are not hashed.
* Fixed TabletSQLite::scan() and remove() to return raw key intead of hashed key.
* Updated TabletLevelDB class using hashed key instead of raw key.