Web Authentication Proposed Recommendation (PR-00)

This tags the commit used as the basis for the published Proposed Recommendation version of WebAuthn Level 1: https://www.w3.org/TR/2019/PR-webauthn-20190117/

Note that the milestones associated with the Proposed Rec effort use "PropRec" in their identifiers rather than "PR" in order to try to reduce confusion with PRs (git pull requests) when referring to them (i.e., the PropRec milestones).

Diffs, change summary, etc. TBD.