Large Tent

I've added a large tent to the game, with a floor space of 3x3 and a total space of 5x5. 

To accomplish this, I added:
- An iuse function for the tent
- An iexamine function to take down the tent
- Two new furniture objects, groundsheets
- The actual json data in item_groups.json, furniture.json, and tools.json

The tent has 40 volume, making it just troublesome enough to outweigh its boon of space. The spawn rate, however, is identical to the smaller personal tent.
Should probably be "this tent" so folks don't get confused between tents.  Little thing, I know.