crane ls should use catalog to list directories

[mattmoor]

Right now it only shows tags :-/

[jonjohnsonjr]

this is high effort low impact

[sding3]

If the argument parses out to be just a hostname rather than hostname/path, would it be reasonable for crane ls to list repos instead listing tags? If this is fine, then it doesn't seem too difficult.

[imjasonh]

crane catalog does what you want today, and lists repos. I think it's best that crane ls and crane.List remain clear about which API they call, and don't try to detect and fallback to call the catalog API.