Add Piece-specific move generation

[Sem1Rose]

If i want to filter the board.GetLegalMoves(); to only get a specific piece's moves, i'd need to use linq to filter the moves based on the type of the move's MovePieceType and StartSquare, which is not very efficient, so it'd be easier if you could add something like board.GeneratePieceMoves() to generate only this piece's moves.

[mcthouacbb]

API changes are no longer accepted after August 1st