A bitboard is a value type wrapping a 64 bit integer which represents
a set of squares on a chess board. Each bit is mapped to a particular
square on the board, 0 -> H1, 1 -> G1,…, 8 -> H2,…, 63 -> A8. For
example if we know a piece to reside on a particular square we can
use a bitboard to to capture the available moves for that piece.