• Integrate with httpcore 0.14
• Update httpx to version 0.21
• Update cli to include new information from "trace" extension.

Release draft: https://github.com/encode/httpx/releases/tag/untagged-d424bd8b5704bf649c40

0.21.0 (15th November, 2021)

The 0.21.0 release integrates against a newly redesigned httpcore backend.

Both packages ought to automatically update to the required versions, but if you are
seeing any issues, you should ensure that you have httpx==0.21.* and httpcore==0.14.* installed.

Added

• The command-line client will now display connection information when -v/--verbose is used.
• The command-line client will now display server certificate information when -v/--verbose is used.
• The command-line client is now able to properly detect if the outgoing request
  should be formatted as HTTP/1.1 or HTTP/2, based on the result of the HTTP/2 negotiation.