Slowly getting DPF Cairo backend up to speed.
Same codebase, totally different targets, same behaviour.
Screenshot shows the Demo/test tool to render a few things, including subwidgets.
(opengl has the nanovg test, which is not possible on cairo for obvious reasons)
Only 2 things left for Cairo backend:
1. load png images from memory (instead of large raw data like opengl side does)
2. get the built-in DPF image widgets compatible with cairo.
Those 2 already done in a PR, but need adjustment