scripts/pypackage.py: added support for using cibuildwheel etc.
scripts/pypackage.py: added support for using cibuildwheel etc.

Added support for using cibuildwheel to build wheels instead of our own
managing of docker instances etc, for example:

    build --cibuildwheel --env 'CIBW_BUILD=cp* CIBW_SKIP="*musllinux* pp*"' ...

Added support for building wheels on native unix, e.g. Linux and OpenBSD.

Always install swig on windows and add to $PATH.

Cope with tar archives where first item does not end with '/'.

Improved matching of python with available wheels - allow abi='none' in
python to match any wheel's abi. This is a workaround for a limitation of our
make_tag() which always uses abi='none'.

Improved quoting of various commands uing shlex.quote().

Support ssh -J jump hosts; see parse_remote(), which now also has some doctest
checks.

Run commands separately when building remotely, gives clearer diagnostics.

Use jlib.untar().

venv_run(): Fixed commands starting with 'py ' when running on windows but not
under cygwin - only use 'cmd.exe /c <command> if running under Cygwin.

env_string_to_dict(): also accept dict or list of strings.

make_sdist(): added <env> arg so one can pass info to setup.py.

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