begin declarative implementation
pass first test by returning zero from score
declare array to hold all rolls
stuff each roll into array
add up all rolls

passes first two tests
refactoring to introduce the concept of frames
split computation of score to multiple lines to handle spares

third test now passes
add computation of score for strike

Test still fails...
skip to next frame if a strike occurs

Must account for the missing rolls (since strikes only have one roll per frame) when indexing into `@rolls`.

This change passes all tests 4 and 5.
Finish declarative example