/cap and /uri are synonyms

[marlowe]

From #tahoe-lafs:

13:58 < warner> I also noticed that /uri and /cap are synonyms.. not sure if that's documented 13:59 < zooko> I had the idea, many years ago, to rename "uri" to "cap" everywhere, but never finished that process... 14:00 < marlowe> warner: if you create the ticket, and assign it to docs, I will make the change 14:00 < warner> I think that synonym came from that process 14:00 * zooko nods 14:01 < marlowe> also, once I finish #1663 we should have a good idea on what is a synonym for what 14:01 < zooko> I had planned to change the Web API docs to direct programmers to the new name -- /cap/ -- and leave the old one for backward-compatibility.