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/hou/README.md

@@ -1,20 +1,20 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./hou syntax-file file-to-process
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -80,7 +80,7 @@ The following regular expression operators are supported:
 For example, one can use the following expression to match a certain declaration
 statement in [hou.c](hou.c):
 
-```<!---re-->
+``` <!---re-->
 	"char"[ *]*[a-zA-Z_][0-9a-zA-Z_]*[ ]*((=[0-9a-zA-Z_ ]+)|(\[[0-9a-zA-Z_ ]*\]))?[ ]*(,[ *]*[a-zA-Z_][0-9a-zA-Z_]*[ ]*((=[0-9a-zA-Z_ ]+)|(\[[0-9a-zA-Z_ ]*\]))?[ ]*)*;
     ```
 
@@ -89,7 +89,7 @@ The regex engine is also algorithmically efficient. To illustrate the point,
 hang for the competing Perl engine while matching itself. Try to compare these
 two engines:
 
-```<!---sh-->
+``` <!---sh-->
     ./hou ansi.txt ansi.txt
     perl patho.pl < ansi.txt
 ```

2012/hou/hint.md

@@ -2,13 +2,13 @@
 
 ### To build:
 
-```<!---sh-->
+``` <!---sh-->
     make hou
 ```
 
 ### To run:
 
-```<!---sh-->
+``` <!---sh-->
     ./hou syntax-file file-to-process
 ```
 
@@ -81,7 +81,7 @@ The following regular expression operators are supported:
 
 For example, one can use the following expression to match a certain declaration statement in hou.c:
 
-```<!---c-->
+``` <!---c-->
     "char"[ *]*[a-zA-Z_][0-9a-zA-Z_]*[ ]*((=[0-9a-zA-Z_ ]+)|(\[[0-9a-zA-Z_ ]*\]))?[ ]*(,[ *]*[a-zA-Z_][0-9a-zA-Z_]*[ ]*((=[0-9a-zA-Z_ ]+)|(\[[0-9a-zA-Z_ ]*\]))?[ ]*)*;
 ```
 
@@ -89,7 +89,7 @@ The regex engine is also algorithmically efficient. To illustrate the point,
 ansi.txt contains a pathological expression [2] that guarantees a hang for the
 competing Perl engine while matching itself. Try to compare these two engines:
 
-```<!---sh-->
+``` <!---sh-->
     ./hou ansi.txt ansi.txt
     perl patho.pl < ansi.txt
 ```