Removal of Autotools in favour of Meson as build system for GStreamer

[Tim-Philipp Müller]

Hi,

The time has come to remove support for Autotools (configure; make) as
build system in GStreamer!

Meson has been the prefered build system for a while now and the
autotools build was officially deprecated with the 1.16.0 release.

The 1.16 stable release series will continue to support both Meson and
Autotools as build system, but we will be removing Autotools in git
master in the next couple of days now that the last missing feature,
building the plugin documentation, has been implemented in the Meson
build.

No doubt there will be some fallout from this, but we need to do this
now so that there is plenty of time to collect, analyse and fix issues
that come up in time for the next release series.

There will be an unstable 1.17.1 development release in the near
future, so that distributors and other downstream users who still rely
on the autotools build have time to update to and test the Meson build
and report any issues.

Adjustments may also be required for the new documentation setup which
has recently moved from per-module documentation built with gtk-doc to
a single documentation build in the gst-docs module using hotdoc. The
plan is to ship the documentation alongside releases in form of a
separate tarball in future.

Developers who still rely on the autotools-based gst-uninstalled
environment should be moving to gst-build which uses Meson to build all
main GStreamer modules in one go and also provides an uninstalled
environment for development purposes. See

  https://gitlab.freedesktop.org/gstreamer/gst-build

for more information.

You can follow our progress in gitlab:

  https://gitlab.freedesktop.org/gstreamer/gstreamer-project/issues/42

Feel free to pop into #gstreamer on the Freenode IRC network if you
have any questions or need help moving to a new development setup.

Cheers
 Tim