Adding coveralls integration

Run coverage with all tests and send results to coveralls.io.
diff --git a/.gitignore b/.gitignore
index ddb969d..cf2c4a6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,8 @@
 
 # Test files
 .tox/
+
+# Coverage files
+.coverage
+coverage.xml
+nosetests.xml