Add tests.
Add the API facade method for backups download.
Add the API client method for backups download.
Add the backups download subcommand.
Send a buffer over that wire rather than a ReadCloser.
Use []byte instead of bytes.Buffer.
Add an HTTP-based download endpoint.
Use HTTP requests in the API client for download.
Drop the old download server implementation.
Merge interfaces for better type checking.
Simplify error handling.
Clean up test a tiny bit.