Adding codecov

Author: michaeltryby

tox.ini

@@ -4,12 +4,14 @@
 envlist = py36
 
 [testenv]
-whitelist_externals =
-  swig
+passenv = APPVEYOR APPVEYOR_*
+whitelist_externals = swig
 skipsdist = True
 usedevelop = True
 deps =
   pytest
   numpy
+  coveralls
 commands =
-  python -m pytest --color=yes epanet_python -s
+  coverage run --source=epanet_python setup.py test
+  coveralls