Split into separate function.
Rename Coappearances class to Appearances.
Initialize hash elements as empty arrays.
Add example for appearances.
Remove unneeded require statement.
Add method to return all pages among all chapters.
Add method to compute coappearances across all chapters.

Also refactored link generation to use a hash instead of inefficiently searching an array of links to look for duplicates. Coappearance for all characters in all chapters can now be computed in under 1 second.