point (name, x, y) {
        this._points.push({name: name, x: x, y: y});
        return this;
    }
**mandatory**

Set up a data point on the overlay. The name of a data point should match a specific 'key' among
data groups generated using keyAccessor.  If a match is found (point name <-> data group key)
then a bubble will be generated at the position specified by the function. x and y
value specified here are relative to the underlying svg.
@param {String} name
@param {Number} x
@param {Number} y
@returns {BubbleOverlay}