The goal is to catch cases where the return value exists, but is
forgotten. There was a large enough number of them to turn this
into a real check. Initially, I just wanted to implement it to fix
the problems, then delete the code. But since this is so common, I
think it is worth the annoyance.
ldoc has a magical `@classmod` module type which tries to detect
what is a method and what is a static function. It fails about as
often as it works. This commit makes everything explicit to remove
such issues.
Fixes#2640
Ref #1373
Emmanuel Lepage Vallee
Lucas Schwiderski
Luke Bonham