Auto-generate the file-level documentation from its contents

[fosterbrereton]

The brief and owner fields in index.md for a class and the file that contains it should be inherited (somehow) from the class documentation itself. When there's a single class in a file, it seems silly to copy the brief and owner up to the index file(s).

Another option would be to make those fields __OPTIONAL__ if there's a single sub-entity in the file. No need to copy if it's just going to be redundant.