TODO:

• Resolve Drop RuntimeError on closing a connection pool with active connections. #631
• Resolve Forwarding HTTP proxies should use a fresh connection for every remote host #637
• Resolve Lazy import either 'anyio' or 'trio' #639
• Create draft release - https://github.com/encode/httpcore/releases/tag/untagged-be7f27eaaf1debf72311
• Add release date to changelog (I'll do this once we've had an approving review and am ready to hit go.)

Proposed changelog...

0.16.3

• Allow ws and wss schemes. Allows us to properly support websocket upgrade connections. (Allow ws and wss schemes. #625)
• Forwarding HTTP proxies use a connection-per-remote-host. Required by some proxy implementations. (Forwarding HTTP proxies should use a fresh connection for every remote host #637)
• Don't raise RuntimeError when closing a connection pool with active connections. Removes some error cases when cancellations are used. (Drop RuntimeError on closing a connection pool with active connections. #631)
• Lazy import anyio, so that it's no longer a hard dependancy, and isn't imported if unused. (Lazy import either 'anyio' or 'trio' #639)