Add missing exceptions for return codes

[jorisdral]

We have bindings in botan-bindings for return codes, but we are missing some higher-level exceptions in botan-low. From what I could see, Botan.Low.Error is missing at least exceptions for

• BOTAN_FFI_ERROR_TLS_ERROR
• BOTAN_FFI_ERROR_HTTP_ERROR
• BOTAN_FFI_ERROR_TPM_ERROR
• BOTAN_FFI_ERROR_ROUGHTIME_ERROR

Alternatively, there may be a reason why this exceptions are omitted. If so, we should find out what the reason is and document it.

[jorisdral]

Note also that it in throwBotanErrorWithCallstack, which converts the error codes to Haskell exceptions, it is easy to miss a case in the case-expression. For example, when a new return code is added. Is there a way we can make the compiler complain if not all error codes are matched on?

[dancewithheart]

Opened PR #134 for this.
I did not address:

it is easy to miss a case in the case-expression

It would make the change harder to review because it likely needs a redesign.

[jorisdral]

It would make the change harder to review because it likely needs a redesign.

That's okay, just adding the missing exceptions is already quite useful