to use the opcodedesc environment.
Changed a \code{} to a \file{} near the start where a file is referenced.
Fixed a typo: "on" --> "one" in ROT_THREE description.
Wherever opcodes were referenced by name, use \code{OPCODE_NAME}; usage was
inconsistent. Ideally, another macro would be defined since these don't
represent code a programmer would type, but that's minor even for me. It'll
probably get converted automatically in the SGML conversion project. Whether
that matters or not isn't relevant at this point.
