Modernize a bit

In particular:

* Depend more on Shepherd and less on the dated document internal database.
* Remove WebSocket section as fetch handles that.
* Move from a priori authenticated to potentially trustworthy.
* Drop the explicit port change as it would always no-op (default port for a scheme is normalized to null on a URL)
* Export the definition Fetch needs to invoke.

Fixes #11, fixes #13, and fixes #18.

Author: annevk