Deprecate some listening options

Those are: captcha, register, web_admin, http_bind and xmlrpc
The option `request_handlers` should be used instead, e.g.:

listen:
  ...
  -
    module: ejabberd_http
    request_handlers:
      "/admin": ejabberd_web_admin
      "/bosh": mod_bosh
      "/captcha": ejabberd_captcha
      "/register": mod_register_web
      "/": ejabberd_xmlrpc

ejabberd.yml.example

@@ -57,19 +57,20 @@ listen:
     port: 5443
     ip: "::"
     module: ejabberd_http
+    tls: true
     request_handlers:
+      "/admin": ejabberd_web_admin
       "/api": mod_http_api
       "/bosh": mod_bosh
+      "/captcha": ejabberd_captcha
       "/upload": mod_http_upload
       "/ws": ejabberd_http_ws
-    web_admin: true
-    captcha: true
-    tls: true
   -
     port: 5280
     ip: "::"
     module: ejabberd_http
-    web_admin: true
+    request_handlers:
+      "/admin": ejabberd_web_admin
   -
     port: 1883
     ip: "::"

src/ejabberd_http.erl

@@ -983,6 +983,18 @@ prepare_request_module(Mod) when is_atom(Mod) ->
 	    erlang:error(Err)
     end.
 
+emit_option_replacement(Option, Path, Handler) ->
+    ?WARNING_MSG(
+       "Listening option '~s' is deprecated, enable it via request handlers, e.g.:~n"
+       "listen:~n"
+       "  ...~n"
+       "  -~n"
+       "    module: ~s~n"
+       "    request_handlers:~n"
+       "      ...~n"
+       "      \"~s\": ~s~n",
+       [Option, ?MODULE, Path, Handler]).
+
 -spec opt_type(atom()) -> fun((any()) -> any()) | [atom()].
 opt_type(trusted_proxies) ->
     fun (all) -> all;
@@ -1004,15 +1016,30 @@ listen_opt_type(certfile = Opt) ->
 	    File
     end;
 listen_opt_type(captcha) ->
-    fun(B) when is_boolean(B) -> B end;
+    fun(B) when is_boolean(B) ->
+	    emit_option_replacement(captcha, "/captcha", ejabberd_captcha),
+	    B
+    end;
 listen_opt_type(register) ->
-    fun(B) when is_boolean(B) -> B end;
+    fun(B) when is_boolean(B) ->
+	    emit_option_replacement(register, "/register", mod_register_web),
+	    B
+    end;
 listen_opt_type(web_admin) ->
-    fun(B) when is_boolean(B) -> B end;
+    fun(B) when is_boolean(B) ->
+	    emit_option_replacement(web_admin, "/admin", ejabberd_web_admin),
+	    B
+    end;
 listen_opt_type(http_bind) ->
-    fun(B) when is_boolean(B) -> B end;
+    fun(B) when is_boolean(B) ->
+	    emit_option_replacement(http_bind, "/bosh", mod_bosh),
+	    B
+    end;
 listen_opt_type(xmlrpc) ->
-    fun(B) when is_boolean(B) -> B end;
+    fun(B) when is_boolean(B) ->
+	    emit_option_replacement(xmlrpc, "/", ejabberd_xmlrpc),
+	    B
+    end;
 listen_opt_type(tag) ->
     fun(B) when is_binary(B) -> B end;
 listen_opt_type(request_handlers) ->