## TODO
* [x] Explore the flickering, seems like when a frame is too different from the previous frame, Termwiz decides to blank the terminal before rendering?
* [x] Make the compositor blend the background colour of text cells with the layer below.
* [ ] Add at least `iMouse` to get cursor/mouse interaction.
* [ ] Get rid of `shaderc` and just use plain `glsl`.
* [ ] Setup user config so users can provide their own shaders.
* [ ] Add extra buffers/channels, to get eg the fish shoal shader working 
* [ ] A setting for making the default foreground colour just inverse whatever background colour it's on?
