Force Field Generator
---------------------

Force field generators repel players and mobs within a given radius from
the generator. The radius can be 5 to 25 and is in all directions. An
'electric dome' appears marking the field. The generator consumes fuel
relative to the radius. A radius of 25 uses 1 coal in 10 seconds, 5 uses
1 coal in 50 seconds. Each time an entity is repelled it cost 1 fuel value
(1/40 of a coal). Any players or mobs permitted inside the field can be
added to the Permit list. Each entry must be on a new line with no extra
spaces. Empty lines (not even a space) are ignored. The mob's registered
name or tag can be used. The owner of a locked generator will not be
repelled. When something is repelled it takes a small amount of damage.

Only the owner can dig or access the form of the locked version.

UI
Channel - digilines channel of generator.
Radius - the node radius to repel, in every direction. 5 to 25.
Permit - list of players or mobs to allow within field. Mobs can be registered
			entity name or tag.
Start/Stop button - starts and stops the field.
Fuel - single slot inventory.
Player inventor - 32 slot inventory at bottom.


Mesecons
	Turns the generator on and off.


Digilines messages

"start"
	Start the generator.

"stop"
	Stop the generator.

"radius n"
	Set the radius to n, where n is a number between 5 to 25.

"add <name>"
	Add a name to the permit list.

"remove <name>"
	Remove a name from the permit list.

"status"
	Query the status of the generator. The generator will send a digilines
	message with its own channel as the following table:
	{
		action = "status",
		state = "on" | "off",
		radius = n, -- radius as number
		permit =
		{
			<list of names>
		},
		fuel =
		{
			name = name, -- eg. "default:coal_lump", will be "" if empty
			count = n, -- count of fuel
		}
	}


Hoppers and pipeworks tubes can be used to push or pull the fuel.