pep-517: remove the `build-backend` key to allow for users to build extensions
PEP 517 changed how projects should define their build dependencies.
The presence of a `pyproject.toml` file changes the behavior of `pip` to
conform to PEP 517.
Since we haven't updated the `setup.py` file yet (I'm not even sure we're not
an edge case which would make it harder/impossible, I have not tried yet), this
is a workaround to issue6589: it allows users to pass `--no-use-pep517` to pip
to revert to the legacy installer. The build backend is simply assumed to be
the `build_meta:__legacy__` one.
Differential Revision: https://phab.mercurial-scm.org/D11393
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install::
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing::
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.
Notes for packagers
===================
Mercurial ships a copy of the python-zstandard sources. This is used to
provide support for zstd compression and decompression functionality. The
module is not intended to be replaced by the plain python-zstandard nor
is it intended to use a system zstd library. Patches can result in hard
to diagnose errors and are explicitly discouraged as unsupported
configuration.