Update tox.ini to check more stuffs (#103)

requirements-test.txt

@@ -0,0 +1,6 @@
+flake8
+flake8-copyright
+isort
+pep8<1.6
+coverage
+

tox.ini

@@ -1,5 +1,19 @@
 [tox]
-envlist = py27,py34,py35,py36
+envlist = flake8, isort, py27,py34,py35,py36
 
 [testenv]
-commands = python -m unittest discover
+deps =
+    -r{toxinidir}/requirements-test.txt
+commands =
+    coverage erase
+    coverage run -m unittest discover
+    coverage report --fail-under=75 --omit=.tox/*,/usr/*
+
+[testenv:flake8]
+commands=
+    flake8
+
+[testenv:isort]
+commands=
+    isort --check-only --recursive --diff num2words tests
+