1) Walk through 2 balls (one frame) at a time.
2) Score is calculated on the fly (i.e. no need to store the state)
Expected error: Expected 16 but was 13.
Implemented calculation of spares.
Rename i variable as it is a bad name.
Refactor out spare detection routine.
Refactor tests.
Expected error: Expected 24 but wsa 17.
Implemented handling of strikes.
Made test more robust to catch bug in spare rountine (missing + sign to accumulate score)