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.

1991/rince/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make all
 ```
 
@@ -11,7 +11,7 @@ that's fewer than the original program.
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./rince
 ```
 
@@ -30,7 +30,7 @@ The author set the maximum number of moves to 484.
 
 ### Alternate build:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
@@ -41,7 +41,7 @@ configurable maximum number of moves allowed, defaulting to the entry's max,
 
 To reconfigure the maximum number of moves to 700:
 
-```<!---sh-->
+``` <!---sh-->
     make clobber MAXMOVES=700 alt
 ```
 
@@ -50,13 +50,13 @@ To reconfigure the maximum number of moves to 700:
 
 To run the first alt version:
 
-```<!---sh-->
+``` <!---sh-->
     ./rince.alt
 ```
 
 To run the second alt version:
 
-```<!---sh-->
+``` <!---sh-->
     ./rince.alt2
 ```