Documentation/libraries-and-tools: add vitess
- [lytics/metafora](https://github.com/lytics/metafora) - Go distributed task library
- [ryandoyle/nss-etcd](https://github.com/ryandoyle/nss-etcd) - A GNU libc NSS module for resolving names from etcd.
- [Gru](https://github.com/dnaeon/gru) - Orchestration made easy with Go
+- [Vitess](http://vitess.io/) - Vitess is a database clustering system for horizontal scaling of MySQL.
