tox.ini: Bring over changes from 1.0-alpha branch

These are the changes that @sigmavirus24 did to `tox.ini` on the
`1.0-alpha` branch in
https://github.com/sigmavirus24/github3.py/pull/287

tox.ini

 [tox]
-envlist = py26,py27,py32,py33,py34
+envlist = py26,py27,py32,py33,py34,pypy,{py27,py34}-flake8
+
 [testenv]
-deps = 
-    requests>=1.2.3 
-    coverage>=3.5.2 
-    mock>=1.0.1
-commands = 
-    python setup.py test
+pip_pre = False
+deps = -rdev-requirements.txt
+commands = py.test
+
+[testenv:pypy]
+deps =
+    -rdev-requirements.txt
+    unittest2
+commands = py.test
 [testenv:py26]
-deps = 
-    requests>=1.2.3 
-    coverage>=3.5.2 
-    mock>=1.0.1
-commands = 
-    python setup.py test
+deps =
+    -rdev-requirements.txt
+    unittest2
+commands = py.test
+
+[testenv:py27]
+deps =
+    -rdev-requirements.txt
+    unittest2
+commands = py.test
+
+[testenv:py27-flake8]
+basepython = python2.7
+deps =
+    flake8
+    flake8-docstrings
+commands = flake8 github3/
+
+[testenv:py34-flake8]
+basepython = python3.4
+deps =
+    flake8
+    flake8-docstrings
+commands = flake8 github3/
 [pytest]
 addopts = -q tests/