* ATC & ASTC support
- Add update format enum for bimg additions
- renderer_gl ATC and ATSC support
- renderer_mtl ASTC support
- renderer_vk ASTC support
- updates to other backends for new enums
- Support emulated ATC
* cleanup
* Add texture_compression test files for ATC/ASTC formats
* Update 'update' example for ATC formats
- Generalise tile code a little
- Add ATC variants
- Ignoring ASTC for now as not emulated -- should we add empty
checkerboard emulate though?
