Check bool parameter is either true or false (after lower)

[JonathanTripp]

• Add test that a boolean command line parameter is one of: 'on', 't', 'true', 'y', 'yes', '1' (for true) or 'off', 'f', 'false', 'n', 'no', '0' (for false) after lower()
• If a flag default is False, then allow --flag to set it to True (so the ==True is unnecessary)
• If a flag default is True, then allow --no-flag to set it to False (so the ==False is unnecessary)