[w3c/webauthn] c112c9: Clarify security model and remove vestiges of "nat...

  Branch: refs/heads/vijaybh/lots-of-fpwd-issues
  Home:   https://github.com/w3c/webauthn
  Commit: c112c9621bdffacb022d57d6b59cecf2a671dc5b
      https://github.com/w3c/webauthn/commit/c112c9621bdffacb022d57d6b59cecf2a671dc5b
  Author: Vijay Bharadwaj <vijaybh@users.noreply.github.com>
  Date:   2016-05-07 (Sat, 07 May 2016)

  Changed paths:
    M index.src.html

  Log Message:
  -----------
  Clarify security model and remove vestiges of "native API" language

Fixes #58 by adding verbiage in the API section about the two layers in
the WebAuthn security model. This discussion is ongoing with the TAG, so
we will open a new issue if there are follow-ups.

Fixes #20, #21, #23 by removing mentions of native apps and APIs, as
these are out of scope for this specification.