much memory, and was inconsistent, especially with input_CreateThread
taking an array of options

* Revert to using array of options

* To add an item with options:
    - either use playlist_ItemNew, ItemAddOption, and then AddItem
      (useful if you don't have all your options in an array)
    - either use playlist_AddExt (use this if all your options are
      already in an array)

* To add an item without options: use playlist_Add

You can still add options after an item has been added by using either
playlist_AddOption or playlist_ItemAddOption

* Attempt to improve API and solve thread safety issues.
  - playlist_Item* functions allow to touch items only.
    p_item->lock must be used when needed
    (playlist_ItemNew, playlist_ItemDelete, playlist_Item*Info,
     playlist_ItemSet* )

  - playlist_ItemGetById and ItemGetByPos give you playlist_items
    for GetByPos, you should have the playlist lock

At the moment, the playlist_Set* and playlist_*Info functions are kept (they work with position) but should be avoided.