For allowing a more ergonomic use and better integration on the
ecosystem, this adds the `std::error::Error` `impl` for our custom
errors.
We intent to drop this hand made code once `derive_more` finishes the
addition of the Error derive support[1]. Until that is available, we
need to live with that.
1. https://github.com/JelteF/derive_more/issues/92
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
