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.

2019/ciura/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
@@ -22,14 +22,14 @@ For more detailed information see [2019 ciura bugs](../../bugs.html#2019_ciura).
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./getwords.sh en | grep .. | ./prog string
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -42,7 +42,7 @@ newline.  See the Author's remarks for more information.
 
 ### Alternate build:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
@@ -54,7 +54,7 @@ Use `prog.alt` as you would `prog` above.
 
 ### Alternate try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.alt.sh
 ```
 
@@ -83,7 +83,7 @@ of the alphabet exactly once.
 
 #### Example execution:
 
-```<!---sh-->
+``` <!---sh-->
     $ grep .. /usr/share/dict/words | ./prog abcdefghijklmnopqrstuvwxyz
     qualm fjord wiz pyx vs beg kc nth
     quartz jinx vs fed kc womb glyph