Implementation of repeatable options

Hi,

I ended up implementing this for a project I'm working on.  I called it magnitude, but could be renamed repeatable or something else.  If there's any feedback, let me know and I can make edits.

The one "hack" is that options that have multiple letters that repeat are assumed to be "magnitude."  I just didn't see any better way to do it.

Tests pass, but I have some more testing to do and see what happens.

Tested on PHP 5.4.30