Add lisp-unit as a module. Use (require :lisp-unit) (or "lisp-unit")

to load lisp-unit.  This also allows the regression tests to be
self-contained so we don't have to have lisp-unit installed via
quicklisp or some other means.

Unlike asdf and defsystem, we do not provide a precompiled fasl.

code/module.lisp:
* Add defmodule forms for lisp-unit

contrib/load-lisp-unit.lisp:
* Module file to compile and load lisp-unit.