Whoops, actually raise an error if we don't know how to get battery capacity.
Include a 'gamify' option, to graph battery life in videogame hearts.

Uses U+2665 for full-heart and U+2661 for open-heart.  Now you can do this:

			{
				"name": "battery",
				"args": {"intervals": 7, "gamify": true}
			},

The "intervals" argument works without "gamify", btw, and defaults to 5.