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.

2012/endoh2/README.md

@@ -1,13 +1,13 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./endoh2 > pi.c
     gcc -o pi pi.c
     ./pi > 314.c
@@ -15,7 +15,7 @@
 
 and:
 
-```<!---sh-->
+``` <!---sh-->
     ./endoh2 e > e.c\
     gcc -o e e.c
     ./e > 271.c
@@ -26,7 +26,7 @@ and:
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -112,7 +112,7 @@ characters and not requiring a return in `main()`.  In fact, recent compilers
 with `-std=c99 -Wall -W -Wextra -pedantic` would say nothing.
 
 
-```<!---sh-->
+``` <!---sh-->
     gcc -std=c99 -Wall -W -Wextra -pedantic spigot.c
     clang -std=c99 -Wall -W -Wextra -pedantic spigot.c
 ```
@@ -123,7 +123,7 @@ and gcc-4.5.3 and clang-3.1 on Cygwin.
 
 ### Synopsis
 
-```<!---sh-->
+``` <!---sh-->
     cc endoh2.c -o endoh2
 
     ./endoh2 > pi.c