Guess checking doesn't properly count double letters

[joshoxe]

A combination of tests need to pass:

• checkGuess only counts double letters once given that a guess has a single letter and an answer has a double letter
• checkGuess only counts double letters once given that an answer has a single letter and a guess has a double letter
• checkGuess only counts double letters once given that a guess has a single letter and an answer has a double letter, and the double letter has full likeness in the 2nd position
• checkGuess only counts double letters once given that a guess has a single letter and an answer has a double letter, and the double letter has full likeness in the 1st position