[w3c/webauthn] e74d8c: Fix #609: Formally define User Handle (#616)

  Branch: refs/heads/master
  Home:   https://github.com/w3c/webauthn
  Commit: e74d8c4da2813559086fa32a28bdc6c576d54c1f
      https://github.com/w3c/webauthn/commit/e74d8c4da2813559086fa32a28bdc6c576d54c1f
  Author: Emil Lundberg <lundberg.emil@gmail.com>
  Date:   2017-10-10 (Tue, 10 Oct 2017)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  Fix #609: Formally define User Handle (#616)

- Formally define User Handle
- Rename "user id" and similar terms to "user handle" everywhere
- Change name and type of `AuthenticatorAssertionResponse` field `DOMString userId` to `ArrayBuffer userHandle`
- `PublicKeyCredentialUserEntity.id` is not renamed, but it is now referred to as the "user handle"

This does not:

- Formally define the term "user account".
- Improve the privacy considerations around returning `userHandle`, as suggested in #578.