[v2.0] Replace exceptions with error codes

[cmannett85]

We sort-of already have precedence for this via utility::result and multi_lang_exception error codes. This will be the first big API change.

There are already 3rd-party libs that implement these but I don't want to add another dependency.

[cmannett85]

This issue makes no sense, if the program input args cannot be parsed then execution must stop - exceptions are the right tool for the job.