Major Feature: NPCs and Talk, Teach, Unteach, and Rig NPC Commands

[seisatsu]

Add an NPC object to the game. NPCs are listed in a room when looking, and have their own names and descriptions. Using the talk command on an NPC switches the player's context to that NPC. Conversation points will be listed out, and using say with one of those conversation points will prompt programmed responses. It will also be possible to rig talking points so that they cause things to happen. Players who are talking with an NPC cannot interact with the current room or the players or objects in it. NPCs will be programmed with the teach and unteach commands.