Support error messages

[ewels]

Currently, error messages from non-existent flags etc are not formatted. It would be good to give these consistent formatting.

I would be surprised if there are also other types of Click output which are also missing.

[ewels]

Looks like error messages are printed by raising a click.UsageError.

Need to track down where these are handled so that we can format printing the output. I guess this will mean monkey patching another function call 😕

[ewels]

Docs about exception handling here: https://click.palletsprojects.com/en/8.0.x/exceptions/

Ah, after a bit of digging, I think this is probably the code that we want to customise: https://github.com/pallets/click/blob/6411f425fae545f42795665af4162006b36c5e4a/src/click/exceptions.py#L39-L43

[ewels]

ok, that worked - got basic support now:

The click function has more complex code for UsageErrors which I haven't ported yet, so will leave this issue open until then.

This code also adds the need for more monkey patching lines, so it'll be better after #10 is merged.

[ewels]

Now finally finished in #10 - working fully as expected I think 👍🏻