You can now pass a dictionary of request headers when starting a new
download in ProtocolServer.
The HTTP and HTTPS protocol will include the headers in their requests.
Apparently that's allowed and the RFC is just unclear about it.
Some servers seem to zero-pad the chunk size for whatever reason, and
previously, we interpreted that as the last chunk.
These are supposed to be interpreted caselessly so let's just use the
case insensitive traits throughout. This means we'll understand things
like "Content-Length" even when they send "content-length" etc.
Contrary to popular belief, not every implementation of TLS follows the
specs.
Some of them just drop the connection without sending a proper
close_notify, and we should handle that gracefully.
Apparently servers will feel free to pad their response if they send one
that contains a content-length field.
We should not assume that the entirety of the response is valid data.
