Update to 0.6.0:

Version 0.6.0
=============

*released on 06 August 2015*

- ``password_command`` invocations with non-zero exit code are now fatal (and
  will abort synchronization) instead of just producing a warning.
- Vdirsyncer is now able to synchronize metadata of collections. Set ``metadata
  = ["displayname"]`` and run ``vdirsyncer metasync``.
- **Packagers:** Don't use the GitHub tarballs, but the PyPI ones.
- **Packagers:** ``build.sh`` is gone, and ``Makefile`` is included in
  tarballs. See the content of ``Makefile`` on how to run tests post-packaging.
- ``verify_fingerprint`` doesn't automatically disable ``verify`` anymore.

(wiz)