Update palette to 0.5

[azriel91]

Bumped dependencies, and updated rendy/examples/meshes to test that it still works.

[azriel91]

Incorporated changes from #265. However I'm sure I'm doing something bad^TM in image.rs -- I don't understand the pixel formats (docs), so simply made it compile.

The sprite example runs though:

cargo run --example sprite --features="base init-winit texture-image shader-compiler vulkan"