Connection: keep-alive

[FreeMasen]

Currently this server doesn't hold open accepted sockets, except for the SSE handler. According to the specification, we should be holding open accepted sockets when the header Connection: keep-alive is part of a request. This will require selecting any kept alive sockets along with the Server.sock property to then dispatch requests as they arrive.

note: This requires that all incoming requests contain a Content-Length header, as chunked encoding is not supported at this time.