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.

1996/eldby/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
@@ -11,7 +11,7 @@ section.
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./eldby.alt
 ```
 
@@ -28,7 +28,7 @@ problematic for some people, can be configured to different speeds by way of the
 value used in `usleep()`. The default is `35000` but you can easily change
 it. To do so try:
 
-```<!---sh-->
+``` <!---sh-->
     make SLEEP=20000 clobber alt
     ./eldby.alt
 ```
@@ -41,7 +41,7 @@ This version is the original which has no sleep time in between updates.
 
 ### Original build:
 
-```<!---sh-->
+``` <!---sh-->
     make all
 ```