Ideas: Add enums, filepath, dirpath, constants

[Swoorup]

Thoughts on adding enums, file path, directory path types to options?
These options allow restricted subset of strings to be passed as flags

[jacobdeichert]

Specifying a list of accepted values for a flag/option could be a nice user experience (preventing typos, documentation).

A file/directory path flag type could be nice as well. We could verify it's correctly formatted before it reaches the script.