This replaces the old hack which was using a local Linux-specific symlink. Now,
the Dynare default is the same as in Sphinx, i.e. rely on a CDN for delivering
MathJax.
Adapt our CI accordingly to continue using MathJax from the Debian package
there (to avoid privacy issues related to the use of a CDN).
- 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/