Added new sample AI - "vixen", improved "basic_python"

I was going to create a highly advanced super AI and not reveal the source code. Then I would win the competition!
But, turns out it is just as shit as all the others, so I added it to git. Also I made the competition, so that seems fairly self defeating.

It was easier to add some extra stuff to basic_python than to force it into the new AI.

"vixen" (where do I get these names? Well, a fox is smart, and a vixen is a fox. Therefore, "vixen" is a smart AI. Q.E.D)

I basically copied asmodeus' "optimised score" and path finding technique, but I changed the way scores are calculated to include probability.
At one point I was adding the scores for paths that began with the same direction. This seemed like a brilliant idea. It was not.

After all this, vixen beats asmodeus some of the time, I haven't tested how often, but each AI has beaten the other at least a few times.
Most of the time vixen loses seems to be due to losing the marshal or general on bom...