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.

1988/isaak/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make all
 ```
 
@@ -11,7 +11,7 @@ code](#alternate-code) below.
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./isaak
 ```
 
@@ -21,7 +21,7 @@ code](#alternate-code) below.
 The original version of this code is in [isaak.alt.c](isaak.alt.c).
 The original entry starts with the line:
 
-```<!---c-->
+``` <!---c-->
     main(){};
 ```
 
@@ -37,7 +37,7 @@ compile.
 
 ### Alternate build:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
@@ -64,7 +64,7 @@ due to the fact that BSD style systems have an `sprintf(3)` that returns a `char
 *`.  Due to the above problems, we placed the output of this program in the
 file: isaak.encode.  To read this file do.
 
-```<!---sh-->
+``` <!---sh-->
     uudecode < isaak.encode
     cat isaak.output
 ```