changed to bxcan >=0.4, <0.6

[pdgilbert]

This PR is to relax the version requirement for bxcan. See discussion at #114 (comment)

[hannobraun]

Thanks for the pull request, @pdgilbert!

The CI build for this PR passes, with bxcan 0.5.0. In your comment you link to your own CI builds. I didn't dig into those, but presumably they build correctly with bxcan 0.4.0. This is all good.

The problem I'm seeing is that this PR adds a new configuration that we're not testing in our CI. Changes to the code in this crate that uses bxcan might expose some of the incompatibilities between bxcan 0.4 and 0.5, which could lead to build failures.

Maybe we could add a build configuration that uses bxcan 0.4.0, using something like cargo update -p bxcan --precise 0.4.0. Not sure if that would work though. I'll just merge this PR, as it addresses a real problem. But if anyone wants to look into the CI issue, that would be very welcome.

[hannobraun]

I just looked into the bxcan changelog and it seems like the only change from 0.4 to 0.5 is the defmt dependency. So I guess my concern is unfounded, and there's probably no way for us to introduce any bxcan-related breakage.