header changes per QUIC PR 1498 + fix warnings

Simplify stream id tests

Partially reliable streams plumbing

Fixes memory leaks

Root certificate setter

Do not select stream when reset was sent

Introduce varint frame types. They do little for now.

Add tests for varint decoding

from memory

Coalesce multiple segments in a packet

Fix client auth

The client sends more data when client authentication is activated, so we can
not switch to `server_ready` in epoch 2.

Align with latest version of picotls -- include change in handling SNI