Add geographiclib.rb

This adds a formula for GeographicLib 1.37.  In the past year GeographicLib has been downloaded 8000 times from sourceforge.  But only 700 of these downloads are for MacOSX.  It's time to make it easier to deploy GeographicLib.
Can probably slim this down to a single command; we just want to ensure it was compiled correctly. :+1: for being thorough, though!