Add a tox.ini to drive tests

tox.ini

@@ -0,0 +1,20 @@
+[tox]
+minversion = 2.9.1
+skip_missing_interpreters = true
+envlist = py27, py34, py35, py36, py37
+
+[testenv]
+description = run the test driver with {basepython}
+commands = python -m unittest discover tests
+
+[testenv:lint]
+description = check the code style
+basepython = python3.7
+deps = flake8
+commands = flake8 -j0 {posargs}
+
+[flake8]
+max-line-length = 99
+ignore =
+  # multiple statements on one line (colon) (we use this for classes with empty body)
+  E701