Add go examples

Code and site changes to support the Go programming language and, specifically, Gophercloud v1.
Hmm, we should probably be consistent in nomenclature with our code, here - it's a "ProviderClient," not an "Identity", and a service client, not a provider. Talking about the region right off the bat also feels a little like starting in the middle.

Also, I think it'd valuable to show a bit more here to highlight the full flow, not just the authentication: provider client, service client, request function from a resource package. I think that would help to show the minimal flow to do the smallest useful thing.

How about:

> To interact with Rackspace using Gophercloud, you'll first need to create an authenticated Rackspace session, represented by a *provider* client. Then, you can use the provider client to obtain a *service* client to interact with a specific cloud service in a given region. The service client can be given to the request functions within that service's resource packages to interact with the service. In this example, we'll interact with the object storage service.

And then expand the example like so:

```go
import (
  "github.com/rackspace/gophercloud"
  "github.com/rackspace/gophercloud/rackspace"
  "github.com/rackspace/gophercloud/rackspace/objectstorage/v1/accounts"
)

provider, err := rackspace.AuthenticatedClient{gophercloud.AuthOptions{
  Username: "{username}",
  APIKey:   "{apiKey}",
}}

service, err := rackspace.NewObjectStorageV1(provider, gophercloud.EndpointOpts{
  Region: "{region}",
})

metadata, err := accounts.Get(service).ExtractMetadata()
```

(We don't have to use the account request, there, I just picked it because I already had that tab open.)