Laplace approximation: filter out non-positive definite Hessians

Closes #1659

See merge request !1666

Shorten block in Tex-citation

See merge request !1665

Avoids arrows from linebreaks introduced by the software

Closes #1659

There were previously two lists of members, which were inconsistent.

By the way, add Sumudu to the list.

We now support Octave ≥ 4.2 only.

By the way, in another test, use the isoctave function instead of manual test.

Previously, if Blanchard-Kahn conditions were not satisfied, there was the
possibility an exception about NaN/Inf values in gy/gu was raised *before* the
exception about BK itself, leading to a confusing message. This commits moves
the test for BK before the test for NaN/Inf in gy/gu.

Closes: #674

In 98bdf765, all XLSX files were removed in
favour of XLS, for compatibility with MATLAB R2009b.

But this broke the very same tests under Octave, since XLS support is not very
good there.

This commit implements a solution that works everywhere, by using XLSX whenever
possible, and XLS otherwise.

Was broken by the previous commit, which renamed some datafile without updating
EXTRA_DIST in tests/Makefile.am.

— use XLS instead of XLSX in testsuite datafiles
— use optimset instead of optimoptions
— use quadv/quadl/quadgk instead of integral
— fix race condition in load_m_file_data_legacy.m tests
— use fallback implementation for intersect(…, 'stable')

Also includes various modernizations.

Some URLs have changed with the new Dynare website.

Also use HTTPS whenever possible.

Mentioning that Octave is a GNU project is pointless and maybe even confusing
for users.

Previously, the solver would recompute the Jacobian at every iteration. But, if
an iteration fails, the current point is not moved (only the radius of the
trust region changes), hence it is not necessary to recompute the Jacobian in
that case. This commit implements this optimization.

When the model is linear, there is no need to reevaluate the Jacobian for each
time period, since it is invariant.

Closes: #1662

Add fallback implementation for contains and splitlines functions.

See merge request !1664

* split up report output, creating new files for the preamble, the body of the report, and each individual page of the report.
* allow the user to set the page number
* allow for the removal of headers and footers from a given page

* The macOS snapshot until this point did not work unless the user had already installed `libmatio`, `gsl`, and `gcc` via Homebrew.
* We are not modifying `m4/ax_matio.m4` as we want to still be able to compile against shared libraries in development

Closes #1478

In particular, mention the Linux Mint and Arch Linux packages.

[skip ci]

shorten test names because adding `_namespace` made some .mod file names too long

[skip ci]