Add some backups testing helpers.
Drop the "archivable" interface.
Add HTTP request helpers to the API client.
Drop a superfluous error return.
Add some doc comments.
Fix up a few error messages.
Use path.Join instead of fmt.Sprintf.
Drop support for insecure HTTP clients.
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.