Key Discovery draft

All,

I updated the Key Discovery editor's draft to use Promises and to support
retrieval of a single named key:
https://dvcs.w3.org/hg/webcrypto-keydiscovery/raw-file/tip/Overview.html

(Yes, I know it should be Promise<any> in the IDL, but I don't think respec
supports this ...)

There have been some requests for APIs to discover multiple keys, for which
I'm waiting on a clear use-case.

...Mark