The interpreter builtins here are almost extraneous. Why?
because the way the interpreter calls existing UnterMUD commands
is almost good enough to do anything you'd need to already. The
reason for having interpreter builtins at all is because they
are much more capable as far as returning values and so forth,
and they can be kept separate from user-level commands.

	To write your own builtins, simply figure out how a node
works (see u.h) and take a look at some of the examples. The
nodes are crushed into an argument vector at call time, with
one being passed as the node into which you can (in fact you
MUST!) place a return value. Avoid like the plague duplicating
any existing cmd functionality - focus on doing stuff that is
hard to do in cmds.