Update example game some, update engine some

* Add RevealAction/UnrevealAction for revealing/hiding items in a room
* Add a lot of checks for items being revealed when it's attempted to be
  triggered
* Implement TeleportAction (mostly)
* For all Check* family of actions, the `yes` and `no` values may be
  just be a single action instead of an array of actions
* Change up how room descriptions and stuff work, mostly so that you can
  specify multiple lines in an array so you can preserve paragraph
  breaks when displayed.
* Example game has some more content

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

examplegame/__init__.py

@@ -7,13 +7,12 @@ from agame.trigger import *
 # This is the *game* here
 database = Database()
 
-from . import items
 from . import rooms
 from . import vars
 
 # Build the game state
 game = Game(
     database=database,
-    room=database.rooms["start"],
+    room=database.rooms["inside_cabin"],
     vars=vars.vars,
 )