Major progress on handling real racket programs.

- Handle regexp literals in the parser.
- Fake-handling of with-continuation-mark.
  (This will work for anything that doesn't try to retrieve
   the marks)
- Add a few more primitives.
  (Need real implementation of quotient/remainder)
- Add meteor test.
- Correctly remember what module we were last processing.

We can now load racket/cmdline successfully.