Read not implemented for &mut [u8]

[Gip-Gip]

I get the following error when trying to read from a &mut [u8]

^^ the trait `embedded_io::Read` is not implemented for `[u8]`
    |
    = help: the trait `embedded_io::Read` is implemented for `&[u8]`
    = note: required for `&mut [u8]` to implement `embedded_io::Read`

It appears that the trait is implemented for &[u8] and not &mut [u8]. That currently causes issues with some code I'm working with, and it should be an easy fix so I'll go ahead and fork+pr.

[Dirbaio]

This is because std::io::Read is not implemented either for &mut [u8]. I just followed that when I wrote that.

I'm curious why is this a problem for you, since it's always possible to convert from &mut [u8] to &[u8].