Let the labeling proc block accept a single word list string

[Michael-F-Bryan]

One of the hackers on Discord caused the Rust compiler to OOM because they pasted 99,000 labels into their Runefile.

Ideally people would use resources for something like this, but the labeling proc block only accepts Vec<&'a str> (i.e. a list of strings). We should give it a set_word_list() method which takes one long string and does self.labels = word_list.lines().collect().