Add meson build system

[tintou]

Add the Meson build system alongside autotools allowing to keep the current build system working until the port is validated by distributors.

The Meson build system has a syntax easier to understand than autotools, build faster
and allow to use ninja instead of make.

It also makes things safer for cross-compilation and dependencies handling.

Keep the autotools CI working as we need both to be proven to work.

[krzk]

This is interesting, I will need a bit of time to review, so don't worry if you do not hear from me - it still will be in todo list.

What I see now is:

1. Your commits need proper description explaining why you are doing, why you have chosen that approach (like keeping automake stuff).
2. How does this interact with existing autoconf/automake? Can we replace completely existing build tools?

[tintou]

I've updated the commit to explain the choice of Meson.

I'm keeping the current autotools build system alive until all distributors have confirmed that there is no regression with the Meson port. Most project that switched to Meson did so during at least one release to allow the distros to fallback to the autotools build system in case something is missing.

[krzk]

OK, thanks for the explanation. I might not have time to review this in next 2-3 weeks, though. Sorry for that, but I want to let you know that it still is relevant thus I hope I will get to that a bit later.

[tintou]

Thank you, no worries, we will soon be arriving in summer with less availability anyway :)

[a-andre]

@tintou Thanks for working on meson build system support. I left a few comments.

[krzk]

Few more comments:

1. Please update also docs documenting how to install using meson (README). Old method (INSTALL) can be kept, maybe renamed to INSTALL.autotools?
2. You might be depending on specific meson version (1.1+?), so this also needs to be part of README. I see CI scripts try pip package in case of older version, is this really a case for some Debians?

[tintou]

Few more comments:

1. Please update also docs documenting how to install using meson (README). Old method (INSTALL) can be kept, maybe renamed to INSTALL.autotools?

2. You might be depending on specific meson version (1.1+?), so this also needs to be part of README. I see CI scripts try pip package in case of older version, is this really a case for some Debians?

1. I've updated the README and renamed INSTALL to INSTALL.autotools
2. Debian Bookworm ships meson 1.0.1 (but 1.7 is in bookworm-backports) and Ubuntu Jammy ships meson 0.61.2. This has been considered as a non-issue by many projects given the ease to install a more recent version with pip if required.