Use 45 degree rotated bitboards for bishop/queen move generation

[jacobgardner]

Some notes before I abandoned the initial implementation to get it working quickly.

        // if file > rank, above the diagonal
        // if above diagonal: 8 - (file - rank) = row #
        // if below diagonal: rank - file = row #
        // if file == rank => row = 0
        //
        //  if above the diagonal, indicies are from
        //      8 - row #  to 8
        //  if below the diagonal, indicies are from
        //      0 to 8 - row #