0.4.0 release

[sosthene-nitrokey]

Updating to the latest heapless release is a breaking change, it might be an occasion to add other breaking changes to a 0.4.0 release.

• Remove the remove method: It is already implemented through Deref in heapless (though in a panicking way), and is unused as far as I know.
• Remove the cbor feature. In can very easily be implemented outside of the crate and is unlikely to be used since the Bytes struct is meant to be used within a struct.
• Remove the from function. It conflicts with the From trait.

Ideally I would even go to the point of removing the Deref trait impl and directly re-implementing all the heapless functions on top of it. This would make the documentation clearer. It would still be possible to implement From/Into a heapless Vec. This would make it possible to deref directly to a [u8].

[robin-nitrokey]

I think this has been solved by #8 and is included in v0.4.0