/webrtc /webrtc-direct rename proceeding

[mxinden]

Tracking next steps to do the /webrtc -> /webrtc-direct rename (multiformats/multiaddr#150 (comment)) with potential for collision with the introduction of /webrtc (browser-to-browser) #79.

• Release fix: Rename Protocol::WebRTC string rep /webrtc to /webrtc-direct #84 as non-breaking change
• Release breaking change from Protocol::WebRTC to Protocol::WebRTCDirect fix: Rename Protocol::WebRTC to Protocol::WebRTCDirect #78.
• Release feat: Add /webrtc protocol (browser-to-browser) #79 as a non-breaking change.