- Added space below non doc-string comments to make it clear
these aren't comments for the symbols directly below them.
- Use doxy sections for some headers.
- Minor improvements to doc-strings.
Ref T92709
This didn't belong on blenlib since it uses DNA data types
and included a bad-level call to BKE_curve.h.
It also meant linking in blenlib would depend on the freetype library,
noticeable for thumbnail extraction (see D6408).
