[wip] New content for gophercloud.io

This hinges completely on #232, but here is a PR that adds up-to-date content for the `v0.2.0` release. Here's our current check-list:

- [ ] Getting Started with Block Storage
- [ ] Getting Started with Compute
- [ ] Getting Started with Identity
- [x] Getting Started with Networking
- [ ] Getting Started with Object Storage