Mining treasure room overhaul!

-Maximum amount of rooms generated raised to 6.
-The size of the rooms is now random, and varies from tiny to quite large.
-Each room is assigned a theme, which determines the turfs it uses and the potential items it can contain.

http://i.imgur.com/THaBBNT.png
Merge pull request #621 from Cheridan/Rooms

Mining treasure room overhaul!