Implement myNew (the new operator)

Implement myNew(Ctor, ...args)

Write myNew(Ctor, ...args) that replicates what the new keyword does:

1. Create a fresh object linked to Ctor.prototype.
2. Call Ctor with this bound to that object and the given args.
3. If Ctor explicitly returns an object (or function), use that instead; otherwise use the object created in step 1.

function Point(x, y) { this.x = x; this.y = y; }
myNew(Point, 3, 4); // { x: 3, y: 4 }, instanceof Point