This commit adds a new protocol command to toggle protocol features

for a client connection. It works like the tag_mask and the associated
tagtypes command.

New commands:

- protocol
  Shows enabled protocol features.

- protocol available
  Show all available protocol features.

- protocol enable {feature...}
  Enables protocol features.

- protocol disable {feature...}
  Disables protocol features.

- protocol all
  Enables all available protocol features.

- protocol clear
  Disables all protocol features.

This commit adds also the first protocol feature.

hide_playlists_in_root
  Disables the listing of playlists in the root folder
  for the lsinfo command.

src/command/AllCommands.cxx

@@ -156,6 +156,7 @@ static constexpr struct command commands[] = {
 	{ "previous", PERMISSION_PLAYER, 0, 0, handle_previous },
 	{ "prio", PERMISSION_PLAYER, 2, -1, handle_prio },
 	{ "prioid", PERMISSION_PLAYER, 2, -1, handle_prioid },
+	{ "protocol", PERMISSION_NONE, 0, -1, handle_protocol },
 	{ "random", PERMISSION_PLAYER, 1, 1, handle_random },
 	{ "rangeid", PERMISSION_ADD, 2, 2, handle_rangeid },
 	{ "readcomments", PERMISSION_READ, 1, 1, handle_read_comments },