Implemented Bowling Kata

Written some tests and implemented the entire bowling kata. 
I like the above method, I would have probably done the same with the if, elsif structure :) But if possible it might be an idea to have methods like is_final_frame?, is_strike? ect. and then call other methods based on that, then have calculate_frame contain only descriptive method names, rather than the actual implementation. That might make it easier to see what you are doing in calculate_frame.

I can't see any obvious flaws though honestly, the above is just a suggestion.
Great work :+1:  :8ball: / :8ball: