Add square_manhattan_distance and square_knight_distance functions

[AInnuganti]

The chess library includes a function called square_distance, which calculates the Chebyshev distance (number of king steps) between 2 squares. This way of measuring distance is not always sufficient though, so I added two new distance functions.

• square_manhattan_distance calculates the Manhattan or Taxicab distance between 2 squares. This is the minimal number of orthogonal king moves it would take to travel from one square to another.

• square_knight_distance calculates the knight distance (using a pretty weird formula), which is the minimal number of knight moves to travel from one square to another

[niklasf]

Thanks! Looks like a useful and consistent addition.

Some tests in test.py (class SquareTestCase) would be good, especially for the knight distance.

[AInnuganti]

Alright both of those changes have been made. I can add some test cases later

[AInnuganti]

I've added tests for square_manhattan_distance and square_knight_distance, and just for good measure, also added some for square_distance. Everything seems to be in working order

[niklasf]

Looks good. Merging.