Add go examples

Code and site changes to support the Go programming language and, specifically, Gophercloud v1.
Make sure to include the imports:

```go
import (
	"github.com/rackspace/gophercloud"
	"github.com/rackspace/gophercloud/rackspace"
)

provider, err := rackspace.AuthenticatedClient{gophercloud.AuthOptions{
	Username: "{username}",
	APIKey:   "{apiKey}",
}}
```