Support FULLGLOBE

[bricelam]

This type seems specific to SQL Server. While it probably won't integrate well with the rest of NTS (i.e. it will throw if you try to do anything with it), it would be nice to support basic I/O scenarios like the prototype in PR #19.

Because this is a singleton type, we might even be able to provide implementations for most members (unless, of course, they depend on the coordinate system).