ForensicError implements std::error::Error by using thiserror::Error

[janstarke]

Every error should implement std::error::Error. For simple conversion, thiserror can be used.

If you do not like having an additional dependency, std::error::Error needs to be implemented manually

[SecSamDev]

I would like to reduce the package dependencies to a minimum. Although thiserror is a very powerful and useful package, in this case std::error::Error could be implemented directly since there are not so many error types.
I don't know how I didn't implement the Error, but you're right, it has to be implemented.
For now we can use thiserror. When I get some time I can look into removing the dependency.