Delete extraneous `require`s.
Delete commented-out code.
Big rewrite, especially for REPL.

- Move the long list of Racket keywords and builtins to its own source
  file.

- Get many things working in the REPL, such as font-lock, indent, etc.

- Derive racket-mode directly from prog-mode. We may as well, because we
  need to define many things for our racket-repl-mode the same way. Note
  that this means a fair amount of code copied from scheme.el, since
  we're doing the whole thing rather than enhancing scheme-mode.
Move code to appropriate sections.

Shared vs. specific to racket-mode vs. specific to racket-repl-mode.
Update (c) through 2014. Bump version to 0.2.
Prevent comint-mode from highlighting input.

Unfortunately this entails copy-pasta of comint-send-input solely to
omit just this one thing. See comment for racket--comint-send-input.
Change buffer name from *racket* to *Racket REPL*.

Also, "namespace" `get-racket-repl-buffer-process` by renaming it to
`racket--get-repl-buffer-process`.
Error message display.

Add semicolon comment prefix to all lines.

Delete dead code since we're no longer showing "stack trace".