This struct implements an Iterator that returns the positions of the 1 bits in the u64.
BitBoard takes this iterator and maps it into Squares in the pieces() method.
This is laying the groundwork for an iterator over the pieces in a Position. 👀
Add some positive tests for these shifts. Negative tests, and boundary tests are still to come.
Implement at custom fmt::Debug for BitBoard so it prints binary.
Use the Direction enum to calculate the neighbor of a square with bounds checking.
Remove the unused rank_index() and file_index methods.
Add Square::from_rank_file and Square::from_index_unsafe to support tests.
Unify the Square*OutOfBounds error types
