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.
But with CMAKE_BUILD_TYPE=None the optimization level is 0?  At least no -O flag is passed to the compiler.  What's the authorized way to get an optimized build?