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/hamano/README.md

@@ -1,20 +1,20 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./hamano < textfile > output.pdf
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -30,7 +30,7 @@ README.md!
 
 That procedure looks like:
 
-```<!---sh-->
+``` <!---sh-->
     ./hamano < README.md > hint.pdf
     cc -xc hint.pdf -o hint
     ./hint
@@ -40,7 +40,7 @@ Another PDF generated is an obfuscated `Hello World!` program (obfuscated inside
 the PDF). Once this is done it will compile the PDF as if it was C (itself!). It
 will look like:
 
-```<!---sh-->
+``` <!---sh-->
     echo 'int main(){puts("Hello World!");}' | ./hamano > hello.pdf
     cc -xc hello.pdf -o hello
     ./hello | cc -Wno-implicit-function-declaration -xc - -o ./hello2