Add rfc7230 test suite and update others to recent Gun

This is a large commit.

The rfc7230 test suite adds many tests from the RFC7230 document.

Gun has been updated quite a bit recently, which broke the Cowboy
suites. This is now fixed with this commit.

A new hook onfirstrequest has been added. It was very useful during
debugging of the test suites.

The initial process code has changed a little; more changes are
expected with the switch to maps for options.

test/handlers/hello_h.erl

@@ -0,0 +1,8 @@
+%% This module sends a hello world response.
+
+-module(hello_h).
+
+-export([init/2]).
+
+init(Req, Opts) ->
+	{ok, cowboy_req:reply(200, [], <<"Hello world!">>, Req), Opts}.