Adding Markdown to Ddoc

[Walter Bright]

On 12/9/2017 9:17 PM, meppl wrote:
> since commonmark exists, is specified and is compatibale to many 
> markdown-languages,  I claim there is a markdown standard: 
> http://spec.commonmark.org/

It certainly wants to be the standard, but until most everyone decides to follow 
it, it is not. There is no list of anyone on that site conforming to it.

Besides, commonmark has a lot of stuff we don't need, like multiple ways of 
doing the same thing.