Add AI difficulty ratings

[coltonw]

I think we want a few AI difficulty ratings, an easy one that will intentionally make some mistakes so a learning player can still beat them most of the time, and then at least a hard one, but ideally a medium then a hard one. We can use the simulation's AI as a baseline for the hard AI.

We also want to when simulating be able to have AIs face each other, rather than re-implementing that AI in the simulation code. In order to prove out that the game is truly strategic, I would like it to be extremely likely (like >90%) chance that a hard AI would beat an easy AI.

[coltonw]

39 may be required in order to make the game truly strategic.

[mturley]

Here's an attempt at a task breakdown for this one:

• [ ] Brainstorm how a difficult AI should behave and how an easy AI should behave
• [ ] Consider if there are any other game mechanics besides AI behavior which should differ when the user selects different difficulties
• [ ] Add mechanism for user to specify difficulty (is this a setting for all games or per-game?)
• [ ] Add code paths to use different AI behavior depending on difficulty (clean code design for AI behavior?)
• [ ] Add support for specifying difficulties of each AI when running simulations
• [ ] Implement different behavior for different difficulties
• [ ] Testing