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>

agame/item.py

@@ -1,5 +1,5 @@
 import dataclasses
-from typing import Mapping, Optional, Sequence
+from typing import Mapping, Optional, Sequence, Union
 from agame.action import Action
 
 
@@ -44,7 +44,7 @@ class ItemInst:
         return self.item.synonyms
 
     @property
-    def room_desc(self) -> Optional[str]:
+    def room_desc(self) -> Optional[Union[str, Sequence[str]]]:
         return self.item.room_desc
 
     @property
@@ -87,7 +87,7 @@ class Item:
     #
     # Otherwise, the `room_desc` string will be colorized and printed as
     # written.
-    room_desc: Optional[str] = None
+    room_desc: Optional[Union[str, Sequence[str]]] = None
 
     # A list of triggers that a game may use. Since this is just a mapping of
     # strings to action sequences, only one set of actions is allowed per