btrfs auto snapshot

Hi,

Appears that no one is working on the auto-snapshot feature for btrfs, so here I am implementing the same.

Below is a draft on the feature list. Any comments / questions / suggestions are welcome, please do let me know.

btrfs auto snapshot feature will include:
Initially:
- configurable timely snapshots
- uses services and crontab to schedule
- Gnome integration
- snapshot rollback and cleanups
- snapshot trashing based on available space
- snapshot destination will be subvol/.btrfs/snapshot@<time> and snapshot/.btrfs/snapshot@<time> for subvolume and snapshot respectively

Later:
-integration with (a ?) backup software
- snapshot trashing per backup confirmation
- rollback from the backup server

Challenges:
- rollback per file or dir instead of entire snapshot-rollback ?
- integrating into the btrfs gui ?
- some FS (samfs) support continues backup
- do we need a new role for the snapshot management ? zfs does.
- we don't need a snapshot if the master file-system didn't change at all
- snapshots are writable by default, hope that sudo-er doesn't modify the snapshot - do we need to implement a kind of read-only snapshot ?

Thanks, -Anand