Introducing.... nukes!

Someone at work today suggested that they might be a neat addition, so there you go. The details:

- They cost 25 jewels.
- They will destroy all of the armies in a city, up to a max of 10.
- If the city had 10 or fewer armies in it and this kills them all, the city will become unoccupied. You should have an army ready to take over the city right after you nuke it.