s/pitchClass/note/g

While "pitch class" is technically correct, "note" is more concise
and easier to understand.
s/answer/guess/g

"Answer" was a bit ambiguous because it could be taken for the user's
answer or the correct answer. "Guess" makes it more clear that this
is the user's answer.
Rename event handler: handleClick -> onClick

This seems like a better naming convention for event handlers.
Merge branch 'rename'