Convert scorer into matrix API. 4% speedup
In i/j loop, pull out terms depending only on i. 7% speedup.

Conflicts:
    src/Scorers.java
Refactor to move loops into a Matrix class. 63% speedup.

This interface is a bit less intuitive for Scorer code, but should allow for
significant savings by more efficient Matrix implementations.

Conflicts:
    src/GameState.java
    src/ScorerTestCase.java
    src/Scorers.java