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.

1985/sicherman/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make all
 ```
 
@@ -11,7 +11,7 @@ more details on it.
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./sicherman < file
 
     echo foo | ./sicherman
@@ -23,7 +23,7 @@ more details on it.
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -43,7 +43,7 @@ audience.
 Although this will be built if the original fails to compile you can do it
 manually like:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
@@ -52,14 +52,14 @@ In this case it will be built as `sicherman.alt`.
 
 ### Alternate use:
 
-```<!---sh-->
+``` <!---sh-->
     ./sicherman.alt < file
 ```
 
 
 ### Alternate try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.alt.sh
 ```
 
@@ -80,7 +80,7 @@ on a line.  Now enter the letters 'n' through 'z'.  But to borrow a quote
 from Richard Stallman: If you think you understand what this code
 does, then you don't, so read it again!  Explain why:
 
-```<!---sh-->
+``` <!---sh-->
     ./sicherman < sicherman.c | ./sicherman | diff - ./sicherman.c
 ```