TravisCI for golang

This is sample of releasing golang project from TravisCI

1. Get source code
2. Run test
3. Send test coverage to coveralls.io by mattn/goveralls
4. Cross-compile by mitchellh/gox
5. Release binary to Github Release by tcnksm/ghr

See .travis.yml. To use this, you need to set GITHUB_TOKEN and COVERALLS_TOKEN in settings tab on travis-ci.org