New API version (HTTP/3)

[WhoSoup]

With the recent publication of the HTTP/3 standard and a variety of API improvements that necessitate breaking changes, it's a good time to make a new API Version: V3.

Unfortunately, golang doesn't a native HTTP/3 library yet, but there are third party packages:
https://github.com/lucas-clemente/quic-go
https://github.com/pion/quic
https://github.com/devsisters/goquic

TODO:

• Evaluate which HTTP/3 libraries to use
• Design new API layout to take advantage of HTTP/3
• Decide on functions to support
• Implement API
• Implement client library