Stats and other fixes

Stat (#152)

* Base statistics gathering and monitoring
* Control rate of HTTP/1 writes (#180)
* HTTP/1 only writes 1 message at a time.
This avoids bloating memory with unsent messages.
This also helps improve the accuracy of our upload stats.
Still needs tweaking to deal with websocket upgrade edge-cases.
* Install websocket handler the moment 101 response comes in, do not wait for stream to complete.
Remove hacks where 101 response completed a stream, no 1xx response should complete a stream.
* Simplify confusing list logic.
Remove the server-only `waiting_stream_list`.
Do a simple scan over available streams to find the next one to work on. This is O(N) when pipelining, but I hear that no one does HTTP/1 pipelining, so in that case O(N=1). We can always re-optimize if we have data that pipelining is super popular and this is a hotspot.
* Update
* Windows warning

Co-authored-by: Michael Graeb <[email protected]>