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.

1998/dloweneil/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make all
 ```
 
@@ -22,7 +22,7 @@ For more detailed information see [1998 dloweneil bugs](../../bugs.html#1998_dlo
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./pootris [X size of board] [Y size of board]
 ```
 
@@ -45,14 +45,14 @@ clockwise `l` does as well. Instead of using `d` to drop the letter you can do
 
 ### Alternate build:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
 
 ### Alternate use:
 
-```<!---sh-->
+``` <!---sh-->
     ./pootris.alt [X size of board] [Y size of board]
 ```
 
@@ -73,7 +73,7 @@ experience may mirror one of our experiences:
 
 ### Usage
 
-```<!---sh-->
+``` <!---sh-->
     ./pootris [X size of board] [Y size of board]
 ```