Add tox config

Author: medecau

tox.ini

@@ -0,0 +1,15 @@
+[tox]
+envlist =
+    py35
+    py36
+    py37
+    py38
+    py39
+    pypy3
+
+skip_missing_interpreters = true
+
+
+[testenv]
+deps = pytest
+commands = py.test {posargs}