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.

1996/jonth/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make all
 ```
 
@@ -24,7 +24,7 @@ For more detailed information see [1996 jonth bugs](../../bugs.html#1996_jonth).
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./jonth :0 :0
 ```
 
@@ -35,7 +35,7 @@ off the other so that you can properly play.
 NOTE: if there is no X service open this will crash. If this is the case you
 might try:
 
-```<!---sh-->
+``` <!---sh-->
     ./jonth
 ```
 
@@ -49,7 +49,7 @@ These are supposed to happen.  As is written in the
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./jonth host1:0 host2:0
 ```