inkex pip install direct from gitlab tarball URL

Added a line in setup.py so we can pip install inkex direct from gitlab tarball URL. I installed my patch like this

# install inkex from my repo archive
pip install --user --verbose https://gitlab.com/biojet1/extensions/-/archive/patch_setup/extensions-patch_setup.tar.gz

To check if inkex is present

python << 'EOD'
from inkex import tester
help(tester)
EOD

To test the installation, extract the full inkscape extensions archive

curl https://gitlab.com/inkscape/extensions/-/archive/master/extensions-master.tar.gz | tar xvzf -
# make sure python will not find inkex in extensions-master
rm -r extensions-master/inkex
rm extensions-master/inkex.py
# test_deprecated* failed in pytest
rm extensions-master/tests/test_deprecated*

Run pytest

cd extensions-master
# direct "pytest" command fails with ImportError: No module named inkex
# but "python -m pytest" command succedes
python -m pytest 

To uninstall

pip uninstall inkscape_core_extensions -y