I do lack sufficient programming skills, so I won't comment on that part (even though C sounds good to me), but I think magnet's approach is a good one! A clearly defined table of things that are "allowed" in the game, and that should/could be used by the players themself to ease their gameplay..
Also, this would minimize the discussions about what is cheating, and what is not, since this information, and those tools, are "approved" officially by creating such a library.
One more thing: I would love if those tools, that could be coded using such a library, were free software. Not only because I love it, but also because the game actually is ported to GNU/Linux (which has a community that is very free software-centered). Also, it is a good way to contribute to the Regnum community itself. Besides: the amount of trust towards such a tool would be much higher if the code were available