[racket-dev] Deprecating collects

> ----- Original Message -----
> I agree that these should never be removed. I would not mind if they
> were marked in some way as "these are here for legacy reasons. New
> code should use XYZ" with specific pointers and helpful advice.

Okay, we will just add the deprecation notices to the documentation
(using the same notice that `htdp/image` and `mzlib/class100` use) but
otherwise won't touch `mzlib` and `mzscheme`.

There are also some libraries that are still in `mzlib` (with pointers
from `racket`) such as `unit` and `control`, so we will go ahead and
move these to `racket` and leave pointers in `mzlib` (but legacy code
should still work) unless anyone has any objections.

Cheers,
Asumu