[w3c/webauthn] 8cc3be: Clean up authenticator processing sections

  Branch: refs/heads/vgb-signature
  Home:   https://github.com/w3c/webauthn
  Commit: 8cc3be6fa8ce0c7b8b150759f1958b056e342e44
      https://github.com/w3c/webauthn/commit/8cc3be6fa8ce0c7b8b150759f1958b056e342e44
  Author: Vijay Bharadwaj <vijaybh@users.noreply.github.com>
  Date:   2016-07-14 (Thu, 14 Jul 2016)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  Clean up authenticator processing sections

Add language about the authenticator needing to produce attestation at
makeCredential time. Fixes #114.

Also add a more complete listing of what is returned from the
authenticator methods. Fixes #105.