Adding Markdown to Ddoc

[John Gabriele]

On Monday, 11 December 2017 at 00:54:00 UTC, Walter Bright wrote:
>
> I have a more pragmatic definition of a standard:
>
> 1. Products that implement it say they adhere to it and defer 
> to it as the authority on correct behavior.
>
> 2. There's more than one such product.
>
> 3. There's more products adhering to that standard than some 
> other competing standard.
>
> So far as I know, commonmarkdown satisfies zero of those.

Looks like Stack Exchange is working on standardizing on 
CommonMark:
<https://meta.stackexchange.com/questions/238957/will-commonmark-be-adopted-for-se/258587#258587>