Allow underline in markdown

[brandonopened]

No description provided.

[roverwolf]

Related to #229 which asked the question of what syntax we want to use to add underlining.

#253 added some HTML tags which allows using <u>...</u> to add underlining.

With this issue, did we want to extend the markdown syntax to add a way to do underlining? If so, we need to determine what syntax we want to use.

[BarbAllen]

Jira #2818

[roverwolf]

PR #305 now parses _abc_ to be dispalyed with <u> instead of <em>

[jmarks]

I want to make sure we are not breaking starndard markdown as defined here: https://github.com/adam-p/markdown-here/wiki/Markdown-Cheatsheet

Underscore before or after, like "test", is strong emphasis. We should use HTML only for underline OR provide a new Markdown for underline. However, neither is a great solution.

[roverwolf]

I think standard markdown would be considered the CommonMark spec.

Underscores before and after normally indicate emphasis (not strong emphasis), which this does break.

What new markdown syntax would you suggest?

One could possibly argue that underlining is a form of emphasis, but the CommonMark spec does specify <em> as the HTML that would be generated (Also note that <u> was deprecated and is technically not "underline" in HTML5).

Please re-open this issue or create a new one if this is a problem as commenting on closed issues is not easily findable and makes it look like the issue is still resolved.