Merge branch 'mauro' into docs-mw

Mauro says:

That's the final series to complete the migration of documentation
build: it converts get_feat from Perl to Python.

V2 is technically identical to v1: the only difference is that it
now uses tools/lib/python/feat to store the library logic.

With that, no Sphinx in-kernel extensions use fork anymore to call
ancillary scripts: everything is now importing Python methods
directly from the libraries.

There's nothing special on this conversion: it is a direct translation,
almost bug-compatible with the original version (*).

(*) I did solve two or three caveats on patch 1.

Most of the complexity of the script relies at the logic to produce
ReST tables. I do have here on my internal scripts a (somewhat) generic
formatter for ReST tables in Python. I was tempted to convert the logic
to use it, but, as this could cause regressions, I opted to not do it
right now, mainly because the matrix table logic is complex. Also,
I'm tempted to modify a little bit the output there, but extra tests
are required to see if PDF output would work with complex tables (I
remember I had a problem with that in the past). So, I'm postponing
such extra cleanup.