Added gemfile, spec page and bowling_game.rb
roll and score methods added along with testing for a 0 score game
Add failing test for case when score is 20
Update roll and score methods for case when score is 20.
refactored out game = BowlingGame.new with let(:game) { BowlingGame.new }
updated score method to be able to calculate a game when a spare is bowled.
Updated the score method to account for strikes.