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.

2012/zeitak/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
@@ -10,7 +10,7 @@ code](#alternate-code) below.
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./zeitak < file
 ```
 
@@ -21,7 +21,7 @@ text files that are not code.
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     make test
 ```
 
@@ -38,7 +38,7 @@ understand this extremely subtle entry.
 
 ### Alternate build:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
@@ -92,7 +92,7 @@ around it's position.
 * Ignores parenthesis inside strings or character constants, so no errors
   will be detected in the following line:
 
-```<!---c-->
+``` <!---c-->
     printf(")");
 ```
 
@@ -104,7 +104,7 @@ around it's position.
 * Escapes (e.g. `\"`) are ignored, so the following line will produce
   an error:
 
-```<!---c-->
+``` <!---c-->
     printf("\"");
 ```