Remove code repetition in spec
Satisfy '1 exact match' scenario
Satisfy '1 exact match' scenario
Satisfy all '1 match' and '2 matches' scenarios

* 1 number match
* 2 exact matches
* 1 exact and 1 number match
* 2 number matches
Correct scenarios

The output for some guesses in the 'all numbers correct' section
were specified wrong.
Satisfy all guess scenarios

Exhaustive unit specs were not necessary to cover all cases.
Extract method object

The Game class was overloaded with two responsibilities:
1) Handle game play.
2) Evaluate guess.

The second responsibility was moved to a new class, Marker.  Specs
for its behavior were migrated to the new class, and a spec was
added to show that Game finds the mark and outputs it.