I would like image to support no_std.

I am using it in the akaze crate. To be able to support embedded robotics/drone targets, it needs to support no_std. However, image is used for the input types to integrate into the ecosystem more cleanly.

This is important for utilizing image across the whole ecosystem, including in embedded targets, where they may have images coming in from attached cameras or even just when reading/writing images being sent over a bus to a screen.

The most basic way to implement this functionality is just to create a std feature that is included by default to allow backwards compatibility. This feature would gate all functions that are specific to an OS. This includes image::open, which can only execute with a file system.

I would also recommend adding a GitHub action to test that no_std support actually works in CI. A good example of this is in some crates I have recently worked on such as eight-point.