feat(pie): Enhance innerRadius option

[netil]

Issue

#856

Details

Implement innerRadius to be applicable for each dataset.

bb.generate({
	data: {
		columns: [
			["data1", 30],
			["data2", 50],
			["data3", 20]
		],
		type: "pie"
	},
	pie: {
		innerRadius: {
			data1: 50,
			data2: 80,
			data3: 0
		}
	}
});