Änderungen

Addition of missing and utility unit & item natives. (#81)

* Addition of missing and utility unit & item natives.

Following extension methods have been defined:

- public function unit.dropItemPoint(item itm, real x, real y) returns boolean
- public function unit.dropItemSlot(item itm, int slot) returns boolean
- public function unit.dropItemTarget(item itm, widget target) returns boolean
- public function unit.useItem(item itm) returns boolean
- public function unit.useItemPoint(item itm, real x, real y) returns boolean
- public function unit.useItemTarget(item itm, widget target) returns boolean

- public function item.isAlive() returns boolean
- public function item.isPickupable() returns boolean