Mutatest

~~~~~

- Added new compare mutation support for:
1. ``Compare Is`` mutations e.g. ``is, is not``.
2. ``Compare In`` mutations e.g. ``in, not in``.

~~~~~

- Initial release!
- Requires Python 3.7 due to the ``importlib`` internal references for manipulating cache.
- Run mutation tests using the ``mutatest`` command line interface.
- Supported operations:

1. ``BinOp`` mutations e.g. ``+ - / *`` including bit-operations.
2. ``Compare`` mutations e.g. ``== >= < <= !=``.
3. ``BoolOp`` mutations e.g. ``and or``.