While implementing these move generators, I realized I was duplicating a lot of code. So, I started thinking about how to do less of that. I create a MoveGeneratorInternal trait that these move generators implement. This trait provides default implementations of several methods.
I also discovered that I needed a way to keep track of move sets per piece for each kind (shape) of piece. The new move generators, and the generators still to come, can now keep track of moves per piece separately in MoveSet instances.
Use the generated knight_moves BitBoards from bitboard::MoveLibrary to generate knight moves.
This commit doesn't yet implement computing bitboards for knight moves.
