Support imports on single file / val args

[verdverm]

Can we support imports for the first arg to:

• transform
• pick, mask

Is there a difference between stdlib and external modules?

[verdverm]

This is largely done where possible, for the glob / filesystem based helpers.

Need to document, wait until other helper funcs are implemented. (Value, String)

[verdverm]

Generally, we are moving towards always loading and handling all inputs the same way. There may still be a difference when the files / values being operated on are top-level list types.