Add coveralls integration

.travis.yml

@@ -1,4 +1,5 @@
 language: go
+
 sudo: false
 
 go:
@@ -7,3 +8,11 @@ go:
   - 1.4
   - 1.5
   - tip
+
+before_install:
+  - go get golang.org/x/tools/cmd/cover
+  - go get github.com/axw/gocov/gocov
+  - go get github.com/mattn/goveralls
+
+script:
+  - $HOME/gopath/bin/goveralls -service=travis-ci