Restart the project based on wgpu-hal

[kvark]

See https://gfx-rs.github.io/2021/07/16/release-0.9-future.html : gfx-rs is technically in maintenance mode now.
We have several choices to proceed:

1. keep using gfx-rs, potentially moving it into this repo
2. drop the Vulkan Portability Initiative
3. migrate to wgpu-hal, potentially rewriting this from scratch

I think we should go with (3), sine wgpu-hal is very solid in itself, and it we only need to take care of essentially 1 code path instead of innovating in each of the backends. So this is the only chance of survival.
Although I'm not sure how to find time to do this... Help would be much appreciated!
We should probably combine this with #31.

[caiiiycuk]

What is the future of gfx-backend-opengl if we go 3? As I know opengl backend exists only in gfx-rs/gfx not in wgpu?

[kvark]

wgpu-hal's OpenGL ES backend not only exists, it's also much superior to what gfx-hal had.
wgpu's examples already run on GLES.