Support detecting request body

[clue]

Proper detection of request message bodies requires:

• Content-Length
• Chunked transfer encoding (Support chunked transfer encoding #96)
• Empty bodies for certain requests

See https://tools.ietf.org/html/rfc7230#section-3.3

This means that we should take these into account and only emit data events for what is actually part of the given request and then emit an end and close event.

This is also a prerequisite for #39.