[w3c/webauthn] 434db0: Fix a few long-standing technical issues (#196)

  Branch: refs/heads/master
  Home:   https://github.com/w3c/webauthn
  Commit: 434db0790daf9d6aee354907ae6e7e86d6e67653
      https://github.com/w3c/webauthn/commit/434db0790daf9d6aee354907ae6e7e86d6e67653
  Author: Vijay Bharadwaj <vijaybh@users.noreply.github.com>
  Date:   2016-09-20 (Tue, 20 Sep 2016)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  Fix a few long-standing technical issues (#196)

* Make credentials unique for each (authenticator, rpId, accountId) tuple

Fixes #25

* Be explicit about errors encountered during processing of the API methods

Fixes #53

* Add detail about error behavior to authenticator model

* Remove namespace collisions with Credential Management by changing Credential to ScopedCredential

Fixes #60