A TiddlyWeb plugin for providing unauthed access to private resources
using "unguessable" URIs.

A URI at a uuid provides an id for a mapping to another URI, internal
to the tiddlyweb server, with the active user being "faked".

This works out okay because:
* only GET is supported
* there's no state that gets carried to the next request

Tiddlers in a bag called PRIVATEER are used to maintain the mappings.
The title of the tiddler is the uuid. The tiddler has two fields:

* uri: the mapped to uri
* user: the user to proxy the action as

An authenticated user can create a new mapping by making a POST
to /_ as either a JSON dictionary with a 'uri' key, or a CGI form
with a uri parameter.

URIs are not checked, you can store what you like and the system
will happily do the internal redirect to it. If junk is stored, a
404 will result.

An authenticated user can list their own mappings by doing a GET to
/_. A JSON dictionary of mappings to uris is returned. Only those
mappings which have a user that matches the currently active user
will be shown.

A user can delete their own mapping by sending DELETE to the URI.