- Change RandomizedMonad to bind by threading a single RandomGen instead of

- Change RandomizedMonad to bind by threading a single RandomGen instead of
splitting the RandomGen.  Threading satisfies the monad laws, and the
parallelizability and evolvability of splitting can still be explicitly
requested via `msplit'.  I think this is a much more logical design!

- Take the opportunity to flesh out independent-list offerings and add comments.