Propose adding cc.Node.position getter/setter

Cocos2d-HTML5 team, please consider adding `cc.Node.position` getter / setter. This makes setting a node's position via setter more "shorthand" and also allows the use of functions which return a `cc.Point`.

Consider this:

    var p = cc.p(100,-50);
    labelHello.x = p.x;
    labelHello.y = p.y;

Versus this:

    labelHello.position = p;

The need for a position attribute is greater when using a custom function which returns a `cc.Point`. Like this:

    labelHello.attr({
        x: centralize(100, -50).x,
        y: centralize(100, -50).y
    });

Versus this:

    labelHello.attr({
        position: centralize(100, -50)
    });

If you like the idea of adding a `position` getter / setter, please consider adding it for all other x/y and width/height properties. Like this:

    labelHello.anchorPoint = cc.p(.5,.5);