Add readme

Sparse but is better than nothing.

Add Cairo

Add Cairo backend that can just render simple paths.

This also cleans up a few other things that were wrong.

Add missing conv.rs file

I forgot to "git add" it.

Add solid brushes, filled and stroked Bezier paths

Add some actual drawing functionality.

Initial commit to start project

At this point, it has the most basic drawing functionality, but it
does draw something.