* scribble/srcdoc: add `class*-doc` and `class-doc` provide forms.
* Add missing require of racket/class which contains the class? predicate.
* Add @history stanza to class*-doc and class-doc scribblings and bump version number in scribble-lib/info.rkt to 1.30.
I couldn't locate gif.rkt in the `file' collection. See a complete working example was helpful to get started. I think it will be as useful for
other Racketeers .(especially beginners like myself).
If gif.rkt is indeed gone due to refactorings, I guess the reference to it should removed.
