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.

2006/night/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
@@ -10,7 +10,7 @@ code](#alternate-code) section below.
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./night
 ```
 
@@ -23,7 +23,7 @@ keys.
 
 ### Alternate build:
 
-```<!---sh-->
+``` <!---sh-->
     make alt
 ```
 
@@ -129,7 +129,7 @@ to deobfuscate.
 Keypad support was removed to save space. To restore, modify the
 following two macros to:
 
-```<!---c-->
+``` <!---c-->
     #define ATG srand(time(0)); initscr(); cbreak(); noecho(); start_color(); keypad(stdscr,1);
     #define AGG A&2?KEY_UP:KEY_DOWN:A&1?KEY_RIGHT:KEY_LEFT
 ```