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/mikeash/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
@@ -18,7 +18,7 @@ For more detailed information see [2005 mikeash bugs](../../bugs.html#2005_mikea
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./mikeash
 ```
 
@@ -28,7 +28,7 @@ under 64-bit (x86_64, arm64) machines too.
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -67,7 +67,7 @@ functions.
 
 Try:
 
-```<!---sh-->
+``` <!---sh-->
     echo '(format t "~s" (+ 2 2 ))' | ./mikeash
 ```
 
@@ -76,7 +76,7 @@ the lack of a newline are due to the somewhat broken implementation of
 the format function. More sophisticated arithmetic expressions may be
 used:
 
-```<!---sh-->
+``` <!---sh-->
     echo '(format t "~s" (* (+ 2 2 ) (- 5 (/ 9 3 ))))' | ./mikeash
 ```
 
@@ -130,7 +130,7 @@ nowhere near
 Basically, the [LISP][] interpreter is good for some basic math operations, and
 for running itself. To do the latter, try this:
 
-```<!---sh-->
+``` <!---sh-->
     ./mikeash < mikeash.c > mikeash2.c
     diff mikeash.c mikeash2.c
 ```