feat: add --markdown formatting

[mmarchini]

Markdown formatting can help users share the results on platforms like GitHub.

Here's an example of a readme generated using eshost -t --markdown ...: https://github.com/mmarchini/proposal-error-stacks/tree/engines-comparison/testcases

[rwaldron]

I prefer to not change the default reporter, but instead add a new reporter.

[mmarchini]

Hi @rwaldron, thank you for the reply. I can make this change. I was mostly trying to avoid duplicated code, but that's not necessary for the new reporter. Are you ok if we have both table and cli-table as dependencies? I remember there was some limitations with cli-table to format as markdown, but I don't remember what it is.