Request: Switch away from Anyhow for the library crate

[laundmo]

Anyhow should only be used for binary crates which won't have dependents.

This is due to the way Anyhow hides the actual error types. As a developer relying on a library, I may want to handle errors returned by library calls depending on what the error actually is, not just the fact there was an error. Anyhow makes that impossible, as it completely strips typing from errors. Note that Anyhow itself agrees with this:

Use Anyhow if you don't care what error type your functions return, you just want it to be easy. This is common in application code. Use thiserror if you are a library that wants to design your own dedicated error type(s) so that on failures the caller gets exactly the information that you choose.

As Anyhow does, i recommend using thiserror. It allows you to easily expose the actual error types using a enum, or define your own.

[robertknight]

To clarify, this is about the "ocrs" crate. I generally agree. There is a balance between exposing useful information for callers and not exposing too many implementation details. For this reason I think it will make sense to separate the internal and external error types.