Conditionally allow mainline winit for external integration purposes

[tasgon]

I'd like to integrate iced UI rendering in other projects, however the usage of the forked winit can break some dependency handling. I've made it so that users can toggle between it and the mainline version through a feature (defaulting to the forked version).

[hecrj]

Since the changes to winit and glutin are experimental and relatively minor, I recently pushed a new 0.4 branch which uses the official winit and glutin releases. I will try to frequently backport all the changes to master there!

Instead of allowing for dynamic switching of dependencies in master, I believe most users should simply rely on this new branch. Would that work for you?

[tasgon]

Just tested your branch, and it seems to work for me. Out of curiosity, are you planning on publishing this version? If it wouldn't be too much of a burden, would it be possible to have versions of this crate in sync with new versions of wgpu and winit on crates.io? If you'd like, I can assist with the updating process as necessary.

[hecrj]

Yes, I have plans to publish 0.4 soon. But before that, I'd like to have the new website ready and the "Architecture" chapters of the book finished.

At that point, it'll be just a matter of coming up with a proper announcement with a nice change log. A lot has happened since the last release!

I'd appreciate any help on these fronts!