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.

2004/vik1/README.md

@@ -1,20 +1,20 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./vik1 [arg]
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./vik1
 
     ./vik1 a
@@ -82,7 +82,7 @@ Compile the source code and link X libraries if necessary.
 The program takes three options which have to be typed in a specific
 order as described below.
 
-```<!---sh-->
+``` <!---sh-->
     Usage: ./vik1 ['a']['d'][#]
 
     a   - Advanced racing in a winter landscape