Implement std::error::Error to ease type erasure

[MaulingMonkey]

Box<Error>::from(...) is implemented by default for anything that implements Error, and ? uses from by default, making this handy for anything dealing with multiple error types.

• Since CI targets 1.24.0, implement the soft-deprecated description()
• Implementing Error requires implementing Display.
• Also ignore warnings about not using &dyn Debug while we're at it.

[Lokathor]

I wanted to go the opposite direction and have it be no_std, but we could probably put this behind a feature flag if so.

I'll let this sit a bit and think on it