Add Rectangle shape

[alistairjcbrown]

Adds in a new Rectangle shape with available bounds_changed event.

This should fix issue #79

import { Rectangle } from 'react-google-maps';

let bounds = new google.maps.LatLngBounds(
  new google.maps.LatLng(-34.04355650412745, 150.99609375),
  new google.maps.LatLng(-33.68321092658006, 151.4300537109375)
);

<Rectangle
  ref="shape"
  clickable={true}
  draggable={true}
  editable={true}
  onBoundsChanged={() => {
    console.log('Bounds changed');
  }}
  bounds={bounds} />

[alistairjcbrown]

Hi @tomchentw - give me a shout if there's anything else needed for this PR.
it should be a fairly minimal change (most of the diff is the built files) and just adds the Rectangle shape in the same was as the Circle.

[alistairjcbrown]

Hi @tomchentw - just thought I'd give this PR a bump - is this good to be merged?

[tomchentw]

TODO: add this in #88

[tomchentw]

Hi @alistairjcbrown , sorry for the late response.
I took a day to rewrite the module from scratch on #88 . It will be great if you could take a look at it. Thanks!

[tomchentw]

Released v2.0.0 and v2.0.1.