mod_admin_telnet: Pretty-print values returned from commands This makes it much nicer to inspect Prosody internals. Existing textual status messages from commands are not serialized to preserve existing behavior. Explicit serialization of configuration is kept in order to make it clear that returned strings are serialized strings that would look like what's actually in the config file. The default maxdepth of 2 seems ought to be an okay default, balanced between showing enough structure to continue exploring and DoS-ing your terminal. Thanks to Ge0rG for the motivation to finally do this.