remove superfluous testing/driver code from class file
Add ‘neighbors_coords’ method to Cell

— revised Cell object to be initialized with row and column numbers
— revised Environment object to include row and column numbers when initializing cells
— Cell#neighbors_coords returns an array of eight neighbor coordinates (one in every direction)

NOTE THAT NEIGHBORS_COORDS RETURNS 8 COORDINATES (regardless of whether there are
eight viable neighbors).  This quirk will need to be accounted for when iterating through the array of coordinates.
remove superfluous testing/driver code from class file
num_living_cells method

In the context of a given environment, num_living_cells (the nunmber of living cells) can be determined at any time.
Merge pull request #3 from alanflorendo/neighbors

Neighbors