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/buzzard/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make all
 ```
 
@@ -21,7 +21,7 @@ For more detailed information see [1991 buzzard bugs](../../bugs.html#1991_buzza
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./buzzard
 ```
 
@@ -37,14 +37,14 @@ code directly so the keys are not made a `-D` at the compiler.
 
 ### Alternate build:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
 
 ### Alternate use:
 
-```<!---sh-->
+``` <!---sh-->
     ./buzzard.alt
 ```
 
@@ -89,7 +89,7 @@ so make sure to convert tabs to spaces before using it.
 
 Usage:
 
-```<!---sh-->
+``` <!---sh-->
     ./buzzard [filename [escape-char [start-x start-yNNN
 ```