doc: add documentation to all the public structs and enums
This makes them show up in the reference, even if the text itself isn't
the most descriptive.
These have been found with
grep -Przon '\n\ntypedef struct.*?\{' -- include
grep -Przon '\n\ntypedef enum.*?\{' -- include
Add public diff print helpers
The usefulness of these helpers came up for me while debugging
some of the iterator changes that I was making, so since they
have also been requested (albeit indirectly) I thought I'd include
them.
