Mutatest

~~~~~

- Added ``--only`` and ``--skip`` with category codes for mutation families.
- Provides CLI selection of mutation types to be used during the trials.

~~~~~

- Added new ``If`` mutation:
1. Original statements are represented by ``If_Statement`` and mutated to be either
``If_True`` where the statement always passes, or ``If_False`` where the statement
is never passed.

~~~~~

- Breaking changes to the CLI arguments and new defaults:
1. Output files are now optional, the default behavior has changed from always writing an RST
file using the ``-o`` option on the command line.
2. Exclusions are still marked as ``-e``; however, now multiple ``-e`` arguments are
supported and arguments must point to a Python file. The argument used to be:
``mutatest -e "__init__.py _devtools.py"`` and now it is
``mutatest -e src/__init__.py -e src/_devtools.py``. There are no longer default
exclusions applied.

- Improved CLI reporting, including selected test counts and line/col locations
for trial results while processing.

~~~~~

- Internal changes to ``Slice`` mutations for clearer categorization and report output.
- Includes clearing names to ``Slice_Swap`` and ``Slice_RangeChange`` for categories.
- Updates operation names to ``Slice_Unbounded...`` with "lower" or "upper".

~~~~~

- Added new slice mutations:
1. ``Slice_SwapNoneUL`` and ``Slice_SwapNoneLU`` for swapping the upper and lower
bound values when only one is specified e.g. ``x[1:]`` to ``x[:1]``.
2. ``Slice_UPosToZero`` and ``Slice_UNegToZero`` for moving the upper bound of a
slice by 1 unit e.g. ``x[1:5]`` becomes ``x[1:4]``.

~~~~~

- Added explicit tests for ``argparse`` cli options.
- Added mechanism to sort reporting mutations by source file, then line number, then column
number.