Enable coverage testing

For whatever reason I couldn't make this work with testr, so at least
for now the tests will have to go through the testtools runner.

.coveragerc

@@ -0,0 +1,7 @@
+[run]
+branch = True
+source = requests_mock
+omit = requests_mock/tests/*
+
+[report]
+ignore-errors = True

.travis.yml

@@ -9,7 +9,10 @@ python:
   - "pypy"
 
 # command to install dependencies, e.g. pip install -r requirements.txt --use-mirrors
-install: pip install -r requirements.txt -r test-requirements.txt
+install: pip install coverage coveralls -r requirements.txt -r test-requirements.txt
 
 # command to run tests, e.g. python setup.py test
-script: python setup.py testr
+script: coverage run -m testtools.run discover
+
+after_success:
+    coveralls

README.rst

@@ -11,6 +11,8 @@ requests-mock
 .. image:: https://pypip.in/d/requests-mock/badge.png
         :target: https://crate.io/packages/requests-mock?version=latest
 
+.. image:: https://coveralls.io/repos/jamielennox/requests-mock/badge.png
+        :target: https://coveralls.io/r/jamielennox/requests-mock
 
 Intro
 -----

tox.ini

@@ -14,3 +14,12 @@ commands = flake8 requests_mock
 deps =
     flake8
     {[testenv]deps}
+
+[testenv:coverage]
+commands =
+    coverage erase
+    coverage run --source requests_mock -m testtools.run discover
+    coverage html
+deps =
+    coverage
+    {[testenv]deps}