Implement sprite_new_with_image to create a Sprite from raw image data

[danhealy]

This creates a convenience singleton method on Sprite to create an Image from raw image data, a Texture from that Image, and finally a Sprite using createWithTexture.

Ideally the Image and Texture classes would be fully exposed to Ruby, but this is beyond my capabilities at the moment.

Example usage (based on motion-flow with motion-game example here https://github.com/andrewhavens/motion-game-with-flow-example ):

# Inside an MG::Scene
Net.get("http://www.rubymotion.com/img/rubymotion-logo.png") do |response|
  dat = response.body.to_data.to_s
  img = MG::Sprite.new_with_image(dat, dat.length)
  add img
end

The above example won't work on Android for two reasons:

1. .to_data is unavailable
2. A hard coded string in Ruby is interpreted differently somehow by the time it reaches this C++ code, I believe because Java strings are UTF-16 by default, but I am not certain.

[Watson1978]

I think Sprite.new should be extended to accept raw data.

• Create Sprite object from file

MG::Sprite.new('skyline.png')
MG::Sprite.new('skyline.png', :file)

• Create Sprite object from raw data

MG::Sprite.new(data, :raw)