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/persano/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
@@ -10,14 +10,14 @@ setting binary mode on `stdout`. See [alternate code](#alternate-code) below.
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./persano p q [num frames]
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -49,7 +49,7 @@ Use `persano.alt` as you would `persano` above.
 
 ### Alternate try:
 
-```<!---sh-->
+``` <!---sh-->
     ./persano.alt 3 16 > knot3-16.gif
 ```
 
@@ -80,7 +80,7 @@ knots](https://en.wikipedia.org/wiki/Torus_knot) to standard output.
 
 ### SYNOPSIS
 
-```<!---sh-->
+``` <!---sh-->
     ./persano p q [num frames]
 ```
 
@@ -98,14 +98,14 @@ cutting it [^1], until it ends up looking just like a circle embedded in R3 [^2]
 
 Sample usage:
 
-```<!---sh-->
+``` <!---sh-->
     ./persano 3 2 1 > foo.gif
 ```
 
 writes a non-animated GIF (a single frame) stream of a rendered trefoil
 knot to the file `foo.gif`.
 
-```<!---sh-->
+``` <!---sh-->
     ./persano 5 2
 ```