Crabby v2.0.0

Several improvements to Crabby's evaluation and search algorithm have increased the playing strength to approximately 2400 elo based on more than 1000 games against sjeng and other engines. The code base is cleaner, more organized, and should be a better example of good Rust code (I Hope!)

Crabby v1.0.0

First release. Crabby currently performs at around 2100 elo based on ~100 games against Fairy-max v4.8