def flag(short_name, long_name, description, &block)
			return define_value(short_name, long_name, description, true, false, block)
		end
def flag(short_name, long_name, description, &block)
			return define_value(short_name, long_name, description, true, false, block)
		end
This defines a command line argument that's either on or off based on the presense
 of the flag.