Fixed warnings in asio_sys

[Dicklessgreat]

From #775 (comment)

Fixed asio-sys/src/bindings/errors.rs
std::Error::description() has been deprecated.
It should be replaced with std::fmt::Display
I found some code duplication in the std::fmt::Display and std::Error trait, so I have combined the code in std::fmt::Display.
This will be a breaking change, is that OK?
The std::Error implementation of LoadDriverError and AsioError is empty, but I think this is necessary for error handling, so I left it.

Fixed src/host/asio/stream.rs
I wondered what to do with the asio_stream field, but decided to ignore the warning as it might be there to extend the lifetime.I am not 100% sure that this is the right way to do it.

[est31]

Thanks!