Draft with CFGeometryCollection and CF compliance

Compliant with [draft geometry proposal] (cf-convention/cf-conventions#115). Code was made compliant by migrating from coordinate indirection versions of code (v0.1.0) so is a bit hard to follow.

Prototype with Coordinate Indirection

The prototype Python code in this version uses coordinate indirection via a coordinate index variable. Break values are inserted into the index to represent polygon holes or parts in multipart geometries. The code was authored by @bekozi. With the project moving away from this kind of coordinate indexing, this release serves to preserve that code.