Minor Revisions

This is mainly a Quality of Life update, packaging all files into a single ZIP and providing each piece with its own movement explanation page. As of current, no pieces have any significant changes to rules (other than establishing that players have to force opponents into checkmate). I'm playtesting changes to the Bird piece to make it more useful. Afterward, I will probably experiment with adding castling to Erlkings and Trees or allowing trees to move one space in any direction instead of just orthogonally.