Implement capturing of nv12 buffers

buffer: Use GR88 for chroma plane

Implement multi-pass nv12 rendering

headless: Implement window_set_plane()

graphics: Add a method to select plane

Add NV12 shader cooking

Cook shaders a bit

meson: Use _GNU_SOURCE

headless: Initialise nv12 buffers

headless: Add scaffolding for choosing nv12 format

Add scaffolding to setting pixel format to nv12

Add option to capture raw frames

Add a way to access the front buffer

Add a headless rendering backend

Add .gitignore

glsl: waveweave: Keep 1:1 aspect ratio

Create graphics toolkit abstraction layer

Take care of some gcc warnings

meson: Mark exec as installable

Add README.md