* Update to rust 1.60.0
* Rename the feature `convert_bytemuck` to `bytemuck`
* Rename the feature `serialize` to `serde`.
* Make use of the "weak dependency" cargo feature
* Set rust-version = "1.60" for all crates
* egui_glow: clipboard, links, persistence & winit are now opt-in features
* Use old 1.51 toolchain instead of bleeding edge
1.52 and 1.53 has problems with incremental compilation,
so some people chose to stay on 1.51 for now.
So let's make sure egui supports 1.51 for a while!
* Update to cint 0.2.2 to get rust 1.51.0 compatability