improve how markdown code language is commented

We added a space between the markdown triple code mark
and language that was enclosed in HTML comments.

So a line of the form:

````
```<!---c--->
````

became:

````
``` <!---c--->
````

This was done to **help** some code see that the HTML comment
string was not a markdown code specifier.   Not all code
understands this after this changed.  For example, `pandoc(1)`
still forms HTML classes of the form "&lt;!---c--&gt;"
when it encounters the above mentioned change.

We also fixed a problem with `2019/dogon/README.md` regarding
a markdown code block.

We also fixed a problem with `2020/yang/README.md` regarding
a markdown code block.

news.md

@@ -107,7 +107,7 @@ We also added to the
 a _"latest_news"_ JSON member whose value is the date
 of the most recent news item.
 
-```<!---json-->
+``` <!---json-->
     "status_date" : "Mon Jan 30 02:28:44 PST 2023",
     "latest_news" : "Mon Jan 30 02:28:44 PST 2023"
 ```