Small organisational improvements

Switched init hooks to OnScriptInit from YSI.

Updated some old documentation for hooks.

Changed the use of GiveWorldItemToPlayer, the item doesn't actually have
to be already in the world for this function to work (the function
actually removes items from the world). The function should be renamed
to GiveItemToPlayer.
Added debug prints and labels to Item

Items now have debug labels created with them if the compile option
DEBUG_LABELS_ITEM is defined.

Added basic debug prints for core functions, callback hooks and
interface functions.