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.

doc/protocol.rst

@@ -1678,6 +1678,44 @@ Connection settings
     Announce that this client is interested in all tag
     types.  This is the default setting for new clients.
 
+.. _command_protocol:
+
+:command:`protocol`
+    Shows a list of enabled protocol features.
+
+    Available features:
+
+    - ``hide_playlists_in_root``: disables the listing of
+      stored playlists for the :ref:`lsinfo <command_lsinfo>`.
+
+    The following ``protocol`` sub commands configure the
+    protocol features.
+
+.. _command_protocol_disable:
+
+:command:`protocol disable {FEATURE...}`
+    Disables one or more features.
+
+.. _command_protocol_enable:
+
+:command:`protocol enable {FEATURE...}`
+    Enables one or more features.
+
+.. _command_protocol_clear:
+
+:command:`protocol clear`
+    Disables all protocol features.
+
+.. _command_protocol_all:
+
+:command:`protocol all`
+    Enables all protocol features.
+
+.. _command_protocol_available:
+
+:command:`protocol available`
+    Lists all available protocol features.
+
 .. _partition_commands:
 
 Partition commands