python-hetzner: Update to new version 0.7.0.

This introduces the following changes:

 - hetznerctl: Fix UnicodeEncodeError in server product name.
 - Support rebooting of vServers.
 - Server now has a new attribute is_vserver.
 - Add a README.md with examples.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>