Provide a way to convert a height above mean sea level (geoid height) to ellipsoid height
Create a Geoid class that can provide the geoid height above the
reference ellipsoid.
There is already a EGM coefficient reader available which could be
re-used for the EGM96 and EGM2008 models.
(from redmine: issue id 192, created on 2015-03-09, closed on 2016-02-10)