0.6.1:
- fix udisks2 external device detection bug: all devices were considered
  external when using `Sniffer` (as done in the udiskie-mount/udiskie-umount
  tools)

0.6.0:
- cache device states to avoid some race conditions
- show filesystem label in mount/unmount notifications
- retry to unlock LUKS devices when wrong password was entered twice
- show 'eject' only if media is available (udisks1 ejects only in this case)
- (un-) mount/lock notifications shown even when operations failed
- refactor internal API
- experimental support for udisks2
