Greeble

Also, could the PR description say whether compression is enabled by default? The description currently sounds like it's disabled by default, but the code seems like it's enabled by default....

Added `X-Contentious` as I expect there'll be various opinions on enabling by default. Also added `C-Dependencies` as the PR adds a dependency on [half](https://crates.io/crates/half) to `bevy_mesh` - although I'm not...

For positions, I'd suggest an AABB-relative unorm16 instead of f16. It's a faff to set up but the worst case error is much lower. I've seen both tried for moderate...