This causes the size of the array to be incorrectly doubled due to the original regex match items being combined with the custom items (i.e. the ones with just 'url' and 'size' keys).
Also rework 'RSSUtils::encode_srcset()' a bit so it looks similar to 'RSSUtils::decode_srcset()'.
* add configurable log level for update daemon (DAEMON_LOG_LEVEL)
* when daemon log level is set to LOG_EXTENDED (2) log queries for feed
update selection