[plt-dev] struct

In SVN, I've made `struct' the name of the form in the `racket'
language that is like `define-struct', except that it binds a
constructor name without `make-' (by default) and a supertype is
specified after the type name without a set of parentheses.

I don't think we reached consensus on switching to `struct', so I
consider the question still open. It seems to be the only contender at
the moment, though, and this way we can try it out.