Experiment with Skia backend

[noelwelsh]

Using Skija create a proof of concept backend for Skia. Following the documentation on creating a backend and using the generic algebras, it should be quite easy to implement at least Layout, Shape, Path, Style, Debug, Size, and Transform.

If you're a proficient Scala programmer but new to Doodle this would be a good way to get started with a very visible impact on the project.

[noelwelsh]

Please keep the issues just for discussing issues, not for what I assume is GSOC discussion.