Support custom encoding/decoding errors

[Kerollmops]

It would be better and easier to debug a program if the BytesEncoding and BytesDecoding traits could return any error type.

To do so we need to modify the Error enum and more specifically the Encoding and Decoding variants to wrap a Box<dyn Error>.

[MarinPostma]

funny, I spent 3 hours debugging an error caused by just that, where a serializing error occured in a SerdeJson...