Log Message:
py-pygit2: updated to 1.5.0

1.5.0:

- New ``PackBuilder`` class and ``Repository.pack(...)``
- New ``Config.delete_multivar(...)``
- New ``Repository.is_shallow``
- New optional ``message`` argument in ``Repository.create_reference(...)``
- Fix truncated diff when there are nulls
- Unit tests & Continuous integration

Breaking changes:
- Fix ``Index.add(...)`` raise ``TypeError`` instead of ``AttributeError`` when
  arguments are of unexpected type