From review (by Sybren Stüvel): use tox for py2/py3 tests

(and updated docs)

README.md

@@ -15,5 +15,5 @@ Python 2.x support may be dropped in the future.
 
 To run the tests just do:
 
-   >>> pip install pytest
+   >>> pip install tox
-   >>> py.test tests/
+   >>> tox

setup.py

@@ -10,8 +10,7 @@ setup(
     license='GNU General Public License v2 or later (GPLv2+)',
     packages=find_packages('.', exclude=['tests']),
     tests_require=[
-        'pytest>=2.9.1',
+        'tox>=2.5.0',
-        'pytest-cov>=2.2.1',
     ],
     zip_safe=True,
 )

tox.ini

@@ -0,0 +1,13 @@
+[tox]
+envlist = {2.7,3.5}
+
+[testenv]
+basepython =
+    2.7: python2.7
+    3.5: python3.5
+
+deps =
+    pytest
+    pytest-cov
+
+commands = py.test