Log Message:
Update ruby-chunky_png to 1.3.3.

1.3.3 - 2014-10-24

* Improve performance of Canvas#crop and Canvas#crop! by doing less memory
  allocations.
* Update to RSPEC 3
* Add CONTRIBUTING.rdoc file.

1.3.2 - 2014-10-18

* Add HSV/HSL color conversions: Color.from_hsl, Color.to_hsl
* Allow empty IDAT chunks to better conform to the PNG standard.
* Small bugfix in image resampling.
* Documentation and code readability improvements.

1.3.1 - 2014-04-28

* Improve performance of Palette.from_canvas.
* Add Color.euclidean_distance_rgba to compare colors.
* Bugix in Canvas.from_bgr_stream.
* Documentation and code readibility improvements.
* README updates, include mention of screencast.