Arvados

Currently, "arv --help" produces output that isn't very helpful.
It should:

• Show calling syntax for generic REST methods, "arv keep", etc.
• Link to http://doc.arvados.org/sdk/cli/index.html (the usage content for this page is in the wrong place but that's a separate story)
• Perform "arv --help" correctly even if token/server configuration is missing
• Add a separate command like "--help resources" or "--resources" for showing a list of resource types (this requires a valid ARVADOS_API_HOST, but can work without a token if the server permits it).