make the constants more easily configurable

[derek73]

Make it easier to adjust the constants for your own purposes. We know we're never going to be perfect for everyone so it should be more easy and obvious how to customize handling. Something like:

HumanName.constants.titles.add('Dean')

Currently the regex for things like initials and nicknames are in constants.py and there's no easy way to change them. Should make the regex configurable too.

[derek73]

I think this implementation works pretty good.