Updated editor's draft for key discovery

All,

I have updated this draft based on the email discussion so far and for a couple of additional items:

- align the API with the pattern uses in the latest WebCrypto API
- specify a NamedKey subclass of Key, adding the name and id attributes as suggested by Ryan. Text for the id attribute is taken from the discussion on ISSUE-25 and a reference to that issue is included
- specify that NamedKey objects are immutable (their attributes and key material never change, except that the key could be removed, rendering the object useless)
- add the use case that was removed from the WebCrypto API
- use partial interface, instead of extends, to add cryptokeys to Window
- add cryptokeys to WorkerGlobalScope as well

The new draft is here: http://dvcs.w3.org/hg/webcrypto-keydiscovery/raw-file/tip/keydiscovery.html#namedkey-interface

Further comments welcome! We will decide whether to publish this on Monday.

…Mark