complex. The new version is smaller and faster. The interface is
unchanged, except that ring-remove now accepts an optional numeric argument
specifying the element to remove.
(ring-rotate): Nuked. It was (a) unused, and (b) totally broken (as in,
any attempt to use it died with a type error, and when I patched it to fix
that I found its algorithm was broken).
(ring-ref): Added doc string.
