Test Gutter Game (failing)
Test Gutter Game (pass)
Test All Ones (fail)
Test All Ones (pass)
Refactor - Extract function roll_many
Initialise the score variable
Test One Spare (fail)
Re-jig the design a smiggin

* Change bowling_game_roll to record the rolls.
* Change bowling_game_score to calculate the score.
Test One Spare (pass)
Refactor to replace comments with functions

* is_spare
* score_spare
* score_normal
Refactor - replace i / roll with frame_index

* Using frame_index fits the problem better than i or roll.
Test One Strike (fail)
Test One Strike (pass)
Refactor - the strike scoring
Test Perfect Game (pass!)

* No changes required for this test to pass