Expose reference of inner anyhow error

[pbzweihander]

It would be great if http_types::Error exposes the reference of inner anyhow::Error.

Especially, when using backtrace feature of anyhow in stable rust, I cannot get backtraces without losing status and type_name information. But if I can get the reference of anyhow::Error, I can without losing information.

[jbr]

Could this be an impl AsRef<anyhow::Error> for http_types::Error?

[pbzweihander]

@jbr I updated the PR with impl AsRef<anyhow::Error> for http_types::Error!

[jbr]

Thanks!