docs: Assorted fixes
- Fix multiple doxygen-style references:
Doxygen docs refer to types with #foo whereas Eolian uses @foo.
In lots of places the old Doxygen docs have been just copied into eo files
without properly translating references.
- Add some missing descriptions:
Empty doc tags like [] should not be used. Please try at least to provide
a single-line comment, and we can improve that later.
There are still lots of empty doc tags, and their authors will be notified.
Test Plan: Only docs change. make doc and DocFX still work.
Reviewers: zmike, cedric, bu5hm4n
Reviewed By: zmike
Differential Revision: https://phab.enlightenment.org/D7976