Adds the Viewport mix-in class to adv3Lite

A Viewport is an object that allows you to look into one room from another when you examine it or look through it (say); this can be used to model windows or CCTV monitors and the like.

VERSION 1
27-Jul-13

Usage: include this extension after the adv3Lite library but before your own game-specific files. The senseRegion.t module must also be present.