HTTP/1.1 pipelining support for the server

According to the spec HTTP/1.1 must be able to handle [pipelined requests](https://en.wikipedia.org/wiki/HTTP_pipelining) on the server, even if it chooses never to initiate it or even send back pipelined responses. We should ensure we're able to handle this eventually in order to comply with the HTTP/1.1 spec. It's not a pressing issue since browsers don't pipeline requests, and most client only do so when opting in to — but we should probably get around to this eventually (:

Start by reviewing the HTTP/1.1 pipelining requirement linked in the issue and the server's request-handling entry points. Determine how multiple requests arriving on one connection are currently handled. Done means the server can accept pipelined requests in compliance with HTTP/1.1, including appropriate tests for the behavior.

Written by the indexing model from the issue text.