I reworked make-ellipsoid-generator and make-ball-generator and added
some new tests with this commit:

https://github.com/gambiteer/srfi-194/commit/d4c4876723a7552f1a9dfbc10bed4afbdcd721bf

I also adapted the code so it works with recent (Github) Gambits.

I invite comments. I intend to make a pull request soonish.

Brad