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.

1984/laman/README.md

@@ -1,13 +1,13 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make all
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./laman <positive number>
 ```
 
@@ -17,7 +17,7 @@
 The program accepts ONE POSITIVE number.  Seeing is believing, so try things
 like:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 
     ./laman 4
@@ -33,14 +33,14 @@ This code should run you in circles.
 Some new compilers (in 1984) dislike lines 6 and 10 of the source, so we changed
 them from:
 
-```<!---c-->
+``` <!---c-->
     ;++f)a[		b<<5|c]		=d++,b+		=e;for(		f=0;f<O
     <<5|c]^		=a[b<<5		|c]^=a[		(k-(b+1		))<<5|c]
 ```
 
 to:
 
-```<!---c-->
+``` <!---c-->
     ;++f)a[		b<<5|c]		=d++,b+=	e;for(		f=0;f<O
     <<5|c]^=	a[b<<5		|c]^=a[		(k-(b+1		))<<5|c]
 ```