Mutatest

~~~~~

- Including ``pytest`` in the installation requirements. Technically, any test runner can
be used but with all base package assumptions being built around ``pytest`` this feels
like the right assumption to call out as an install dependency. It is the default behavior.
- Updated ``controller`` for test file exclusion to explicitly match prefix or suffix cases
for ``"test_"`` and ``"_test"`` per ``pytest`` conventions.
- Changed error and unknown status results to console color as yellow instead of red.
- Added multiple invariant property tests, primarily to ``controller`` and ``cache``.
- Added ``hypothesis`` to the test components of ``extras_require``.
- Moved to ``property`` decorators for internal class properties that should only
be set at initialization, may add custom ``setters`` at a later time.
- Fixed a zero-division bug in the ``cli`` when reporting coverage percentage.

~~~~~

- Addition of ``optimizers``, including the new class ``CoverageOptimizer``.
- This optimizer restricts the full sample space only to source locations that are marked
as covered in the ``.coverage`` file. If you have a ``pytest.ini`` that includes
the ``--cov=`` command it will automatically generate during the clean-trial run.

~~~~~

- More behind the scenes maintenance: updated debug level logging to include source file
names and line numbers for all visit operations and separated colorized output to a new
function.

~~~~~

- Updated the reporting functions to return colorized display results to CLI.

~~~~~

- Added new mutation support for:
1. ``AugAssign`` in AST e.g. ``+= -= *= /=``.
2. ``Index`` substitution in lists e.g. take a positive number like ``i[1]`` and
mutate to zero and a negative number e.g. ``i[-1] i[0]``.

- Added a ``desc`` attribute to ``transformers.MutationOpSet`` that is used in the
cli help display.
- Updated the cli help display to show the description and valid members.

~~~~~

- Added new mutation support for ``NameConstant`` in AST.
- This includes substitutions for singleton assignments such as: ``True``, ``False``,
and ``None``.
- This is the first non-type mutation and required adding a ``readonly`` parameter
to the ``transformers.MutateAST`` class. Additionally, the type-hints for the
``LocIndex`` and ``MutationOpSet`` were updated to ``Any`` to support
the mixed types. This was more flexible than a series of ``overload`` signatures.