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.

2019/giles/README.md

@@ -1,20 +1,20 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./prog infile.wav outfile.wav
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -62,7 +62,7 @@ Interesting fact: The size of the program from `./iocccsize -i` is 2019.
 
 #### How to use:
 
-```<!---sh-->
+``` <!---sh-->
     ./prog input [output [size [dry [wet [damping]]]]]
     prog.exe input [output [size [dry [wet [damping]]]]]
 ```
@@ -87,7 +87,7 @@ The default settings are designed to make the effect obvious rather than subtle,
 so it may be a good idea to adjust the ratio of "dry" to "wet", to give a more
 pleasant result:
 
-```<!---sh-->
+``` <!---sh-->
     ./prog in.wav out.wav 1.8 80% 15%
 ```