Get rid of all instances of List[HelpDoc].

[hollinwilkins]

Overview

zio-cli used to use a List[HelpDoc] as the error type when validating input arguments to represent multiple help docs to display to the user. This is no longer required because of the HelpDoc.Sequence type, which allows joining two HelpDocs together. This change gets rid of all instances of List[HelpDoc] and replaces them with HelpDoc.

Summary of Changes

1. Find and replace all instances of List[HelpDoc] with HelpDoc
2. Get rid of all cons operations in validate methods

Notes

1. The only time the master code created List[HelpDoc] was with a cons operation to Nil, which means we were never returning more than one HelpDoc in the error channel
2. The only references to HelpDoc.Sequence in the code are in pattern matches, which means we never any instances of this value for now

[CLAassistant]

All committers have signed the CLA.

[jdegoes]

We have to keep HelpDoc.Enumeration, as it is intended to be rendered as a bullet-point list.

On the other hand, HelpDoc.Sequence is intended to be rendered as stacked blocks (like multiple paragraphs on a page).

Otherwise, looks good!

[jdegoes]

We need to keep HelpDoc.Enumeration because it is intended for bullet-point lists.

[hollinwilkins]

Ah, understood, I will restore it :)

[hollinwilkins]

Restored the HelpDoc.Enumeration and supporting code

[jdegoes]

@hollinwilkins Awesome work!