* luaplaylist.c: add support for meta data info. Playlist items now use .path and .name (instead of .url and .title as those are used for meta data).
* luaplaylist/dailymotion.lua: add support for "description" and "arturl" meta data items.
* luaplaylist/*lua: update source to make it work with new playlist conventions.
* luaplaylist/youtube.lua: update help instructions.