Make manpages (#405)

• man: Use doxygen2man to make the API manpages

• [build] drop unused target

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

• [build] update gitignore

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

• [docs] make build -j safe and drop unnecessary dox config files

Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>

• man: Use doxygen2man to generate *.h.3 man pages

so we don't need to use the awful doxygen ones

Co-authored-by: Fabio M. Di Nitto <fdinitto@redhat.com>