chore(tox): add pypi-publish

Hello dear contributors,

This is an auto generated modification to help you improve the code base of logilab. If this commit is bad don't hesitate to close this MR and report it.

Kind regards,

tox.ini

@@ -6,3 +6,18 @@
 deps = -rrequirements-test.txt
 commands =
   {envpython} -c 'from logilab.common import pytest; pytest.run()' -t test {posargs}
+
+[testenv:pypi-publish]
+basepython = python3
+skip_install = true
+whitelist_externals = rm
+deps =
+  twine
+passenv =
+  TWINE_USERNAME
+  TWINE_PASSWORD
+commands =
+  rm -rf build dist .egg .egg-info
+  python3 setup.py sdist bdist_wheel
+  twine check dist/*
+  twine upload --skip-existing dist/*