Obnam: client for server

Goal I have an HTTP API on the server, at least enough of one to be able to try to use the server for chunk storage. My goal for today is to change the Obnam client to be able to use that server at all. It doesn't need to be integrated yet, that can come later. However, the client should be able to store a chunk, retrieve it, delete it, and find chunks based on label metadata. Plan Implement obnam…