Drop deprecated "fixie:" prefix from built-in command line arguments.
Test coverage for the 3 reserved command line arguments: --NUnitXml, --XUnitXml, --TeamCity.
Add --parameter command line option for specifying arbitrary key=value pairs. Demand that all "--" options be recognized as built-in.
Custom parameters specified with key=value syntax must have a non-empty key.
Test coverage for custom paramter parsing in the event that multiple equals signs appear in the key=value part.
Command line option names are case-insensitive.
Update command line argument usage help text.
Improve error reporting for invalid command line arguments.