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.

2004/hibachi/README.md

@@ -1,13 +1,13 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     cd build; ./hibachi-start.sh &
 ```
 
@@ -42,7 +42,7 @@ There is a `hibachi.tgz` file (NOTE: this file was removed by the judges after
 extraction) that unpacks several support files and a subdirectory tree
 containing the documentation and examples. It can be viewed by:
 
-```<!---sh-->
+``` <!---sh-->
     tar -zxf hibachi.tgz
     lynx hibachi/localhost/index.html
 ```
@@ -58,19 +58,19 @@ To build just the executable:
 
 For Cygwin, FreeBSD, Linux (newer), Mac OS X:
 
-```<!---sh-->
+``` <!---sh-->
     gcc -o hibachi hibachi.c
 ```
 
 For Linux (older):
 
-```<!---sh-->
+``` <!---sh-->
     gcc -DSHUT_WR=1 -o hibachi hibachi.c
 ```
 
 For SunOS:
 
-```<!---sh-->
+``` <!---sh-->
     gcc -o hibachi hibachi.c -lnsl -lsocket
 ```
 
@@ -88,20 +88,20 @@ examples. In which case the preferred build commands are:
 
 To start the server on the default port (8008):
 
-```<!---sh-->
+``` <!---sh-->
     cd build;
     ./hibachi-start.sh &
 ```
 
 To test the server:
 
-```<!---sh-->
+``` <!---sh-->
     lynx http://localhost:8008/
 ```
 
 To stop the server:
 
-```<!---sh-->
+``` <!---sh-->
     kill %1
 ```