Wht fuck is this

This is a MapMap data structure, is something like:

	const mapMap = new Map('key', new Set());

but better. It takes care to create SETS automatically on set, and remove keys where the SET is empty, it inherits MAP, so all MAP method are available, obviously.

Usage

	const MapMap = require('map-map');

	const mapMap = new MapMap('parentKey', 'key', 'value'); 
	console.log(mapMap.entries());
	// { [ 'parentKey', Map { 'key' => 'value' } ] }

	mapMap.set('parentKey', 'key-1', 'value-1');
	console.log(mapMap.entries());
	// [ 'parentKey', Map { 'key' => 'value', 'key-1' => 'value-1' } ] }
	
	console.log(mapMap.size()); // 1
	console.log(mapMap.size('parentKey')); // 2

	mapMap.clear('parentKey', 'key-1');
	console.log(mapMap.entries());
	// { [ 'parentKey', Map { 'key' => 'value' } ] }

	mapMap.clear('parentKey');
	console.log(mapMap.entries());
	// {}

	mapMap.clear();
	console.log(mapMap.entries());
	// {}

	console.log(mapMap.has('parentKey')); // true
	console.log(mapMap.has('parentKey-1')); // false
	console.log(mapMap.has('parentKey', 'value')); // true
	console.log(mapMap.has('parentKey', 'value-1')); // false

	mapMap.delete('parentKey');
	console.log(mapMap.entries());
	// {}

	mapMap.delete('parentKey', 'key-1');
	console.log(mapMap.entries());
	// { [ 'parentKey', Map { 'key' => 'value' } ] }

	mapMap.forEach(console.log);
	// Map { 'key' => 'value' }

	mapMap.forEach('parentKey', console.log);
	// 'value'
	// 'value-1'

Cool, no!!?