Rewrite to use a Scheme disassembler by Göran Weinholt.

Code originally from https://github.com/weinholt/industria
and licensed under the BSD license.

Lightly edited to make `fcdisasm.rkt` a #lang racket program,
to move some library references, and to remove non-x86
architecture support (since none of the architectures Racket
supports are included).