Set up coverage.py. Refs #4.

.coveragerc

@@ -0,0 +1,6 @@
+[run]
+source = contextlib2
+branch = 1
+
+[report]
+omit = *test*

.gitignore

@@ -10,3 +10,4 @@ MANIFEST
 *~
 .coverage
 coverage.xml
+htmlcov/

.travis.yml

@@ -17,6 +17,8 @@ matrix:
         - python: pypy
           env: TOXENV=pypy
 
-install: pip install tox && tox --notest
+install: pip install tox coveralls && tox --notest
 
 script: tox
+
+after_success: coveralls

tox.ini

@@ -1,18 +1,17 @@
 [tox]
-envlist = py26, py27, pypy, py33, py34, py35, py36, pypy3
+envlist = py{26,27,33,34,35,36,py,py3}
 skip_missing_interpreters = True
 
 [testenv]
-commands = {envpython} test_contextlib2.py
-
-[testenv:py26]
-deps = unittest2
-
-[testenv:py27]
-deps = unittest2
-
-[testenv:pypy]
-deps = unittest2
+commands =
+    coverage erase
+    coverage run test_contextlib2.py
+    coverage report
+deps =
+    coverage
+    py26: unittest2
+    py27: unittest2
+    pypy: unittest2
 
 [testenv:pypy3]
 # Known incompatibility: https://bitbucket.org/pypy/pypy/issues/1903