Break up room and corridor generation into generate and apply phases

- Generate creates rooms and corridors, and apply applies them to a tile grid.
- Add up and down stairs generation to the Room Generators.
- Clean up Room.wall_points and Room.floor_points to make it easier to
  write a generic apply() method on RoomGenerator

erynrl/map/__init__.py

@@ -17,7 +17,10 @@ class Map:
 
         self.generator = generator
         self.tiles = np.full(tuple(size), fill_value=Empty, order='F')
-        self.generator.generate(self.tiles)
+        generator.generate(self.tiles)
+
+        self.up_stairs = generator.up_stairs
+        self.down_stairs = generator.down_stairs
 
         # Map tiles that are currently visible to the player
         self.visible = np.full(tuple(self.size), fill_value=True, order='F')