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.

1988/robison/README.md

@@ -1,20 +1,20 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make all
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./robison 80 10
     ./robison 40 16
 ```
 
 The first and second parameters are optional.  You might also try:
 
-```<!---sh-->
+``` <!---sh-->
     ./robison 80 2   # <--- can you find the bug?
     ./robison 80 -246
 ```
@@ -24,7 +24,7 @@ The first and second parameters are optional.  You might also try:
 
 The following might make an interesting benchmark:
 
-```<!---sh-->
+``` <!---sh-->
     ./robison 100
 ```