This is a partial revert of 8fa4c483f9.
Actually, the official name is “GNU Octave”, and it is easier to find it under
that name in search engines. So use the full name at a few prominent places,
and use the shorter “Octave” everywhere else.
- integrate with autoconf/automake, so that "make html pdf" now build the
manual
- remove the old texinfo manual
- the PDF manual is now called dynare-manual.pdf (Closes#1543)
- add a Gitlab CI job that updates the online unstable manual under
www.dynare.org/manual-unstable/