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/litmaath/README.md

@@ -1,13 +1,13 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./litmaath some text
 ```
 
@@ -17,7 +17,7 @@ code](#alternate-code) section below.
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./litmaath eschew obfuscation
 ```
 
@@ -31,7 +31,7 @@ a file.
 
 ### Alternate build:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
@@ -40,7 +40,7 @@ Use `litmaath.alt` as you would `litmaath` above.
 
 ### Alternate try:
 
-```<!---sh-->
+``` <!---sh-->
     ./litmaath.alt six was afraid of seven because seven eight nine
 ```
 
@@ -50,7 +50,7 @@ Use `litmaath.alt` as you would `litmaath` above.
 Note the unusual structure:
 
 
-```<!---c-->
+``` <!---c-->
     while (<condition>)
 	     ;
 ```
@@ -66,7 +66,7 @@ could make the body of the `while` loop an `fprintf` with interesting
 variables like:
 
 
-```<!---c-->
+``` <!---c-->
     fprintf(stderr,
 	 "argv=%lo *argv=%lo **argv=%c argv[1]=%lo *argv[1]=%c argc=%d\n",
 	 (long) argv, (long) *argv, *argv && **argv ? **argv : '@',