fix: Rename webrtc-w3c to webrtc and webrtc to webrtc+sdp-munging

[achingbrain]

Summary

Following on from https://github.com/multiformats/multiaddr/pull/150 and an replacement for https://github.com/multiformats/multiaddr/pull/151

Renames:

• /webrtc-w3c -> /webrtc - AKA browser to browser
• /webrtc -> /webrtc+sdp-munging - AKA browser to server

Discussion:

• This option comes from comments on https://github.com/multiformats/multiaddr/pull/151
• It got a lukewarm reception on the triage call so it's presented as an option along with https://github.com/multiformats/multiaddr/pull/152
• Adding +sdp-munging makes it more explicit about the differences, though admittedly there are other differences that aren't encapsulated in the name
• People were uncertain about universal understanding of the term "SDP munging"

Before Merge

• [ ] Allow at least 24 hours for community input
• [ ] If this is a new protocol, has the change been applied to https://github.com/multiformats/multicodec as well? If so, please link the multicodec PR.

[achingbrain]

Closing in favour of https://github.com/multiformats/multiaddr/pull/152