[racket] Reading racket files

"read-accept-lang" and "read-accept-reader" seem to do most of the work.

There is still a few details to attend to.  What McFly Tools currently 
does before calling progedit for the simpler case of "info.rkt" files 
only is to identify one of 3 different formats: no module, #lang, and 
"(module ...)", and go from there.  ("#lang" seemed to introduce a 
"#%module-begin" that "(module ...)" didn't.)

McFly Tools punts on whether an alternative reader (e.g., "at-reader") 
might be in effect where it makes its edits, although "progedit" does 
have a "#:write-stx" argument with this problem in mind.

Neil V.