errors such as TokenizationError is not part of the api but should

What is necessary is to expose all error types through `roffio/__init__.py` and ensure that error conditions are given the correct exceptions.

Start with roffio/__init__.py and inspect the project’s error definitions and the conditions that raise them. The work is done when all error types, including TokenizationError, are exposed through the package API and error conditions raise the correct exceptions.

Written by the indexing model from the issue text.