Adding Markdown to Ddoc

[meppl]

On Sunday, 10 December 2017 at 06:20:43 UTC, Walter Bright wrote:
> 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.

I think these are wrong criterias to estimate the value of 
commonmark. Commonmark doesn't need to list anyone and doesn't 
need to be listed by anyone to be a standard. commonmark is a 
standard proven by following "facts":
1) whenever a language feature is used by all popular markdown 
languages, it is standard
2) there are markdown features who are used by all popular 
markdown languages
3) everyone can reveal this matter of fact - e.g. by writing it 
down as a specification
4) any language feature published by the commonmark-spec is used 
by all popular markdown languages
ergo: commonmark == standard markdown
well, at least, if the commonmark people did their homework right

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

I am not the one who is implementing it, so I will not argue 
against this.