- Enable tests

- Update to 0.4.4:
* Changed how any return value from the ``on_data`` callable is processed. In
earlier versions, the return value was ignored. In this version, if the
return value is ``False``, the data received from ``gpg`` is not buffered.
Otherwise (if the value is ``None`` or ``True``, for example), the data is
buffered as normal. This functionality can be used to do your own
buffering, or to prevent buffering altogether. The ``on_data`` callable is
also called once with an empty byte-string to signal the end of data from
``gpg``.
* Added an additional attribute ``check_fingerprint_collisions`` to
``GPG`` instances, which defaults to ``False``. It seems that ``gpg`` is
happy to have duplicate keys and fingerprints in a keyring, so we can't be
too strict. A user can set this attribute of an instance to ``True`` to
trigger a check for collisions.
* With GnuPG 2.2.7 or later, provide the fingerprint of a signing key for a
failed signature verification, if available.
* For verification where multiple signatures are involved, a mapping of
signature_ids to fingerprint, keyid, username, creation date, creation
timestamp and expiry timestamp is provided.
* Added a check to disallow certain control characters ('\r', '\n', NUL) in
passphrases.