Typos fix.
 Support for finding snapshot by name and getting last snapshot.
Perliminary version of RestoreWorker
Restore: take which hosts to read/write from arguments
RestoreWorker:

1. Support for specying which hosts to read/write.
2. Download in parallel.
Execute sstableloader
Comma separate the target hosts
Print human sizes
Merge pull request #8 from EverythingMe/feature_restore

WIP: Restore backup feature