Add impl From<bincode::Error> for std::io::Error

[imp]

There is a reverse conversion, but this one is missing. It will help quite a lot when used with ? operator.

[glehmann]

that would also make bincode::Error compatible with custom_error.
If there is no opposition to adding this feature, I may give it a try and propose a pull request.

See lovasoa/custom_error#21

[ZoeyR]

implementing From<bincode::Error> for std::io::Error would be a lossy conversion. There are many error cases that would just get thrown away and From really isn't meant for lossy conversions