Added trace-define, trace-let, trace-lambda

Someone asked me about Chez-like trace macros in Racket, even pointing me to this post on the mailing list: http://lists.racket-lang.org/users/archive/2013-October/059735.html

But it looks like they never made it in. So I hacked them up.
Need to handle the case when no name is provided and `syntax-local-infer-name` fails. I think we should just error then.