Npc

1)Created a NPC (non_player_character) that has coordinates and appears on map.

2) I recognize that the numbers which are randomly generating NPC coordinates are magic numbers and prefer it that way by design. Ultimately, there will be certain regions where certain NPCs will appear, in such case they will all be hard coded in and annotated in comments.
How about:

```ruby
[@character, @non_player_character].each do |character|
  mark_character_coordinates(character, terrain)
end
```