add 'num_living_neighbors' property to Cell object
Add Shape Tests

add spec for three life-forms
still-lifes: block, beehive
periodic:  blinker
Add NEIGHBORS and TICK methods to Environment— environment determines the number of living neighbors for each cell (at time T) and assigns that number to a cell-property— environment#tick method implements the rules of LIFE— environment#tick_indefinitely animates the tick/rules with a pause between each animation so it is watchable
add driver code to animate certain shapes
add spec for Rules 1-4
refactor tick method to make apply all rules in a single iteration (rather than cell by cell)
remove 'dies' and 'regenerates' methods
refactor tick method
revise spec to account for refactored cell methods
Merge pull request #4 from alanflorendo/tick

Tick