[webauthn] new commits pushed by vijaybh

The following commits were just pushed by vijaybh to 
https://github.com/w3c/webauthn:

* Cleaned up exposition of processing rules (#154)

* Replace facet with origin

Facet was a holdover from the old FIDO specs and origin is the term 
used
everywhere in this spec (as well as in recent FIDO specs)

* Clean up explanation of computing clientDataHash and passing to 
authenticator

Fixes #153

* Remove text from authnsel extension to avoid chicken-and-egg problem

Fixes #152

* Address comments from @equalsJeffH
  by Vijay Bharadwaj
https://github.com/w3c/webauthn/commit/62b67c02a37ab54ca8b3c1f7606bb7351298ddec