Improve error reporting

https://github.com/apache/incubator-ponymail-foal/blob/4def8545bb894f1890f46d5a2628c54cb6e98831/tools/plugins/textlib.py#L40

It's not ideal for utility methods to use print to signal errors, as the caller has no choice as to whether the message appears or not. Also the function currently can return two different types. Callers need to check the return type on every call.

It would be easier for callers if the function raised an error instead.

Start at tools/plugins/textlib.py around line 40 and inspect the callers of the utility method to understand its current return values and error handling. Update the behavior so errors are raised consistently and callers no longer need to check for alternate return types; done means errors are delivered to callers instead of printed.

Written by the indexing model from the issue text.