rpnChilada 8.4.0

Revamped the prime number operators, and filled in a couple of missing ones.

A number of operator names have changed for more consistency. The old names have been added as aliases.

Added the 'bitwise_xnor', 'from_french_republican', 'to_french_republican', 'to_french_republcan_name' operators.

A fix was made to support using rpn on OS X.

A number of bugs were fixed, and I did extensive touch-ups based on pylint.