Expand Environment

add spec to test expansion methods
add spec to verify environment grows when a rocket is cultured
Environment#expand_if_needed

Expand environment by a row if a living cell is in the last row
Expand environment by a col if a living cell is in the last col

NOTE: This expansion only occurs at the outer edges (max_row and max_col) of the environment. The environment does not expand in a negative direction simply because living cells are located int he first row or column.
add glider shape in 4x4 environment to test expansion methods
Merge pull request #6 from alanflorendo/expand

Expand