Adds feature for skipping include of doxygen headers into sphinx build
when env variable is set.
Builds incomplete docs (no function API documention)
but speeds up building (20min to 1<min).
Add this fast build as the default way of building docs in CI on
non protected branches.
Some errors (for example the errors caused by macro values, as fixed in previous
commit) get logged to stderr even if WARN_LOGFILE is set, but Doxygen succeeds.
Regression in fbb54184ef006ae6644d0b52878414ec0b2af652, the dictionary
passed to generate_doxygen function was still the project_description
structure.
