Fix resolving choice labels

[Zacqary]

Closes #27

Bladeink-compiler will now properly parse choice labels as read counts:

== k ==
+ (first_choice) [Select this choice first]
Ok
-> k
* {first_choice} [Now this should be available]
Before this PR, this choice would not have been available
-> DONE

Since using choice labels as conditionals was previously a no-op, I don't think this qualifies as a breaking change.