Generate qualified Result type in derive

[andrenth]

This prevents problems with generated code when there's an alias for a crate-specific Result type, i.e. type Result<T> = std::result::Result<T, MyError>.

[VictorKoenders]

Thanks!

Just out of sheer interest, how easy did you find it to go through the bincode_derive crate and figure out where you had to change things?

[andrenth]

It was pretty easy to find, but honestly I didn't even have to go through the code, because a grep Result derive/src/* pretty much told me what to do :)