Some refactor ❤️ to an old friend

[3zcurdia]

Why

We all know the motto "If it works don't change it", and in fact I have proven this by recently using this gem into a project. However I noticed that my contributions years ago weren't the cleanest solution. So I decide to give some love to this beloved project, by adding some modern features and improving the readability for future users.

• Include new bundler gem defaults
• Split domain colors logic
• Implement ImageLoader
• Enable extension through downsampler classes
• Improve tests with real fixtures
• Shared examples for downsamplers

[3zcurdia]

My primary motivation behind this PR is to improve readability and scalability of the project. Apparently this his an abandoned project, so I tried to cleanup a little so future readers find the fork and use it from it.