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 propose you do anything at this point but it's worth remembering that generators are Iterables too, but you won't get the desired behaviour. I suggest we cross that bridge if we ever need to call `unscale` with a generator of values.