Inventory system

[culacant]

Redguard's inventory is pretty simple, an outline:

• Items are defined in ITEMS.INI, documentation on the fields is in this file too.
• One item can be selected at a time (special case for sword+potion?)
• Some items can be used, they call a script from the mapscripts to do stuff
• Inventory can be opened in-game, this pauses the game and shows bitmaps of the items in the inventory
• Items in the inventory UI can be inspected, this displays a 3d model and plays an RTX sound

[Thane5]

I already made a basic inventory system (See #7 ) a while ago, maybe we can reuse some of that