Error types do not implement Error::source

[Aeledfyr]

Both the ErrorKind type in bincode 1.3.3 and the EncodeError/DecodeError types in bincode 2.0.0-rc.1 do not implement the source method in std::error::Error, which allows for automatic introspection of error causes.

Implementing it in 1.3.3 should be trivial, as it should be possible to reusing the implementation of the deprecated cause method (which 1.3.3 implements).

I've noticed that bincode 1.0 appears to have a MSRV below the version in which source was added. Does this prevent the library from implementing it in any form, or can conditional compilation be used to implement it if the compiler version supports it?

[VictorKoenders]

I agree this is a good idea. I've implemented this for bincode 2 in #530.

Bincode 1 is in maintenance mode, we don't plan to add new features in the foreseeable future.