Flatten HTTP handler config (#2662) (#2663)

Differentiating middleware and responders has one benefit, namely that
it's clear which module provides the response, but even then it's not
a great advantage. Linear handler config makes a little more sense,
giving greater flexibility and simplifying the core a bit, even though
it's slightly awkward that handlers which are responders may not use
the 'next' handler that is passed in at all.

modules/caddyhttp/rewrite/rewrite.go

@@ -25,7 +25,7 @@ import (
 
 func init() {
 	caddy.RegisterModule(caddy.Module{
-		Name: "http.middleware.rewrite",
+		Name: "http.handlers.rewrite",
 		New:  func() interface{} { return new(Rewrite) },
 	})
 }