Improvements to block device for publishing to crates.io

[andreeaflorescu]

• [ ] https://github.com/rust-vmm/vm-virtio/issues/31
• [x] https://github.com/rust-vmm/vm-virtio/issues/47

[walksanatora]

... I was wondering why this was not on crates.io

[walksanatora]

(any other virtio-block drivers or do i have to try and write my own)

[walksanatora]

... nvm I couldn't use this even If i wanted because I need a #![no_std] virtio device driver