Changed defaults and CLI arg behavior with improved reporting

Breaking changes to the CLI arguments and new defaults:

• Output files are now optional, the default behavior has changed from always writing an RST file using the -o option on the command line.
• 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.