_splitNode(node, width, height) {
    node.used = true;
    node.down = {
      x: node.x,
      y: node.y + height,
      width: node.width,
      height: node.height - height
    };
    node.right = {
      x: node.x + width,
      y: node.y,
      width: node.width - width,
      height
    };

    return node;
  }
Split a node

@param {object} node         Node
@param {number} width        Width
@param {number} height       Height
@returns {object} node       Node