[0.16] Move off error_chain

[kw217]

error_chain was great, but it's a bit outdated now. We should move to anyhow/thiserror or other modern error approach.

[zihadmahiuddin]

I've just started trying this library and noticed that I can't use the ? operator with the Result type I normally use in my projects (which comes from eyre). I get errors saying some Error type (one defined by the error_chain macro I assume) doesn't implement the Sync trait. What do you think about using eyre? Or maybe error-stack once it's possible to use without the nightly toolchain.

EDIT: Now that I think about it, it might not be a lot more beneficial to use eyre over anyhow so maybe that will be just fine.

[kw217]

Error handling is still quite an active area in Rust; whoever picks this up should take a careful look at the landscape before choosing a library. It should be mature and widely used, and ideally on track to becoming (de-facto) "standard".