add goveralls test coverage

for #92

.travis.yml

@@ -10,4 +10,11 @@ go:
   - 1.2
   - 1.3
   - 1.4
-  - tip
+  - tip
+  
+before_install:
+  - go get github.com/axw/gocov/gocov
+  - go get github.com/mattn/goveralls
+  - if ! go get code.google.com/p/go.tools/cmd/cover; then go get golang.org/x/tools/cmd/cover; fi
+script:
+    - $HOME/gopath/bin/goveralls -service=travis-ci