[w3c/webauthn] 9c60ee: Add links to two previous working drafts (#834)

  Branch: refs/heads/master
  Home:   https://github.com/w3c/webauthn
  Commit: 9c60eedd5bf0eb4e77895498447e0c2c8ada4aa8
      https://github.com/w3c/webauthn/commit/9c60eedd5bf0eb4e77895498447e0c2c8ada4aa8
  Author: Angelo Liao <huliao@microsoft.com>
  Date:   2018-03-12 (Mon, 12 Mar 2018)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  Add links to two previous working drafts  (#834)

merging per @AngeloKai's request

* fix proper subset tweak

* resolve linking error for AttestationNotPrivateError

* resolve linking error: idl ref not found for [[DiscoverFromExternalSource]](origin, options, sameOriginWithAncestors)

* remove unnecessary commits

* accept jeff suggestion

* added links to two previous WDs