Max todos

[Tril]

BTW one of the next things we need to work on is Products and Sums of
Spaces...  products are required for one thing, sums for another, and I
think sums might be useful for making a Max space of sets... We might as
well try it and see if it helps.

I'm trying to hold off doing any major changes until we get together,
but I did write tests for and make pointers into a space today... I'll
still be going through the TODOs and thinking about how to proceed in
each one and what order to do them.  (I have a bunch of TODOs for after
1.0, but I thought you wouldn't want to see them so I haven't put them
in the main todo.txt yet)