Make out-of-tree build work

See merge request !63

Adapted to the new master from a patch sent by @cfoyer

    When building out of tree as the, make sure that target refer to
    relative paths.

    This commit also clean-up the usage of the flags and defines
    a per-target definition of flags (can be changed for a
    AM_CPPFLAGS if the global definition is good enough).
Signed-off-by: Clement Foyer <cfoyer@cray.com>

Also adds Clement to the authors list.

Out-of-tree builds are popular when one doesn't want to pollute the
source tree with objects. It also helps debug build setup issues.

- hide echo command but not echo itself
- fix dist-hook useless if not building doc and creating error on make
  dist

Better flags for CI

See merge request !65

Sometimes the CI fails on configure, make sure we capture the log file
for those cases.

Recursive makefiles do not propagation automake flags (AM_CFLAGS),
making the proper configuration of the whole build chain more complex
than it needs to be. This patch goes back to a single makefile.am in
src, simplifying the build quite a bit.

One more silent error. ax_pthreads will fail on -Werror, so we still
need to fix that.

Still fails, some issues in configure.ac/Makefile.am

Note that this still fails on make check, some problem with
CPPFLAGS/LDFLAGS

There's an actual bugfix on tilings in there, as well as extra type
mismatches.

Less than perfect types for the most part, plus a few unused variables.

Some string.h definitions only appear if _GNU_SOURCE is defined, which
is done for us in config.h. As usual, only include this in the .c files,
and first in the header.

Vector implementation was lacking some rigor. Note that it is a bit
tricky to use an int for the `na` element and size_t for an index.

Caught by a fun warning about weird function-pointer-to-int conversion.

We've recently received messages indicating that some compiler
environments out there would choke on some of the code. Let's try to
make the code as C99 compliant and as reliable as possible by activating
more warnings and breaking the CI on it.

autoconf macros fail on -Werror -Wall because of unused variable
warnings, so we deactivate those.

Improve checkpatch workflow, fix the resulting errors

Closes #43

See merge request !67

Pretty straightforward.
Close #43.

Generate the list of source files automatically, to ensure that we don't
miss something.

Improve configure script, header includes

See merge request !64

MAP_ANONYMOUS is only visible in _GNU_SOURCE code. Ensure the config
header is included first so that this symbol appears.

Our code relies on _GNU_SOURCE in a couple of places, so make sure we
call it. Take this opportunity to reorder and clean up the configure.ac
config a bit.

[doc] fix contributing link

Closes #38

See merge request !62

Closes #38.

Also adds a caption to the toctree.

fix doxygen version on readthedocs

See merge request !60

fix CI

See merge request !59

Run in nix env

See merge request !58

remove recommonmark

See merge request !57

Fix CI pipeline

See merge request !56

Readthedocs on branch

See merge request !55

Dist release

See merge request !50

* events triggering a pipeline on master will create aml-latest dist release
* events on branches v.0.0.x will also trigger the pipeline and create a release archive aml-0.0.x.tar.gz
* new tags will trigger the release pipeline and if tag match vx.x.x then it will create a release aml-x.x.x.tar.gz
* Whenever a branch, tag is updated and a release exists, only the link to dist archives is update. Description will remain the same, but can be updated withe the script release.sh

In order to work, the release pipeline still needs to export a RELEASE_TOKEN with rights on gitlab api.