Move anyhow to dev-dependencies?

[Adam Perry]

For the library crate at least it would be cool if it exported a type that implements std::error::Error without type erasure (thiserror is a nice way to do this). Context:

`https://github.com/dtolnay/anyhow#comparison-to-thiserror

EDIT: It looks like anyhow is only used in doctests and examples. Maybe it could be moved in the Cargo.toml to make that clearer?

[Rich Kadel]

Fixed