Add shape of earth 1 and 7

This PR extends `ellispsoid` to handle `shapeOfTheEarth` value `1` and `7`.

This is a precursor to GDT 4/5.
I don't think we need this -- none of the other helper routines are testing this, and it only guards against an obvious coding error, not possible file contents :  If you do pass the wrong section, I think it will just barf on the unfamiliar key names.