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.

2011/eastman/README.md

@@ -1,13 +1,13 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./eastman
 ```
 
@@ -19,7 +19,7 @@ NOTE: to restore your cursor in your shell, try `reset`.
 Run the program. Quit it (ctrl-c/intr). Resize your terminal window. Run it
 again. Try doing this a number of times with different sizes each time.
 
-```<!---sh-->
+``` <!---sh-->
     ./eastman
 ```
 
@@ -60,7 +60,7 @@ program is running, though.  It only checks the size once, when it starts up.
 
 To compile:
 
-```<!---sh-->
+``` <!---sh-->
     cc -lm eastman.c
 ```