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.

2005/vik/README.md

@@ -1,20 +1,20 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./vik [file.map]
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./vik maze.map
 ```
 
@@ -60,7 +60,7 @@ Compile the source code and link in [X
 libraries](https://en.wikipedia.org/wiki/Xlib) if necessary. The program takes
 three options which have to be typed in a specific order as described below.
 
-```<!---sh-->
+``` <!---sh-->
     ./vik [-w <width>] [mapfile]
 ```
 
@@ -75,20 +75,20 @@ where:
 
 Start the engine using a built in labyrinth and texture bitmaps:
 
-```<!---sh-->
+``` <!---sh-->
     ./vik
 ```
 
 Start the engine and loads the labyrinth defined in the file
 [maze.map](maze.map):
 
-```<!---sh-->
+``` <!---sh-->
     ./vik maze.map
 ```
 
 Start the engine using [maze.map](maze.map) in a window that is 400 pixels wide:
 
-```<!---sh-->
+``` <!---sh-->
     ./vik -w 400 maze.map
 ```