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.
We specifically want this CMAKE_BUILD_TYPE as it makes it use our own CFLAGS rather than the CMake defaults.