Profile Image Generator

I've added the profile image generator to the code. To use it, simply pass a hash like this to the constructor:

    user = {
      name: 'Username',
      const_win_rate: "32.2%",
      arena_win_rate: "69%",
      ranking: 25
    }

    image = ProfileImage.new(user).image

In order to see the image, simply do `image.write('test.png')`
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