FSet now has CHAMP sets and maps!

I have just released FSet 1.6.0, which completes the work on CHAMP sets and maps that I started months ago.

CHAMP is a hash-based data structure by Michael Steindorfer, that improves a little on Phil Bagwell's widely-used HAMT.  (The HAMT is used, for example, by Clojure.)

See the GitLab MR  for the details of how to use it.

I did some quick micro-benchmarking, using sets of integers, comparing CHAMP against my older weight-balanced trees.  On lookup (testing whether a value is in the set), CHAMP is about 40% faster at size 4, growing to over 3x faster at size 2048.  On update (adding an element to the set, with about a 25% chance that it's already there), CHAMP has about a 20% advantage at size 4, growing to 40% at size 2048.

So to summarize, there's a significant and welcome improvement in update performance, and quite a remarkable improvement in lookup performance.  W00t!