Add a feature of whether we can move in both directions.
Take into account the possible spawn cases in the evaluation function.
Use logs for features computations.

For example, the evaluation now considers 8-2-8 as bad as 512-128-512.
This greatly improves scores.
Store base-2 logs in a cache. Simulations are 14% faster now.
Put new weights found by cross-entropy.
Add a player that repeatedly does right, up, left, down.
Improve features weights again.
Add a feature that tries to avoid game-over.
Add more information to game dumps.
Display worst best tile after multiple runs.
Artificially load a game from a dump.
Initial implementation of expectimax