Fix for websocket server reading Sec-WebSocket-Key in wrong place when missing, and handling common mistakes from clients

[SoylentGraham]

#12

This is a fix for SimpleWebTransport attempting to read the websocket handshake key "Sec-WebSocket-Key: " from the response headers, but

• Some servers respond with different case (typically. Sec-Websocket-Key instead of Sec-WebSocket-Key).
  • Specfifically in our case, Ngrok sends Websocket
    -gr: I can't remember off hand which is the correct case, but that's a little irrelevent when established servers & clients send the wrong things
• The code previously didn't actually check if this required header was missing, and thus would read the key from -1 + offset, which is obviously wrong. (could read out of bounds & throw, could just read garbage)
  • As it's a requirement, I made it throw.

[SoylentGraham]

Small update on this, ive rewritten in my fork a chunk of this to do proper http header parsing and the code is far far cleaner.