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.

2014/endoh1/README.md

@@ -1,20 +1,20 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./prog > foo.c
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
@@ -36,14 +36,14 @@ What is the difference between running `./prog` and `main`?
 Big terminals with tiny fonts have their uses in certain cases.
 One of them is:
 
-```<!---sh-->
+``` <!---sh-->
     make treacl
     ./treacl
 ```
 
 which is shorthand for:
 
-```<!---sh-->
+``` <!---sh-->
     ./prog < prog.c > treacle.c
     make treacle
     ./treacle

2014/endoh1/spoilers.md

@@ -18,7 +18,7 @@ Do you think that it is possible to write QR code encoder in C within *1kB*?
 It is known that we can mitigate the quine restriction by `eval`.
 For example, this is a quine written in Ruby:
 
-```<!---ruby-->
+``` <!---ruby-->
     eval s="print 'eval s='; p s"
 ```
 
@@ -122,7 +122,7 @@ The compiler tool chain is the following.
 
 You can run the process by `rake` command.  `ruby-minisat` gem is needed.
 
-```<!---sh-->
+``` <!---sh-->
     $ gem install ruby-minisat
     $ rake
 ```
@@ -145,7 +145,7 @@ but it appears to no longer exist.
 
 You can use [tool.rb](tool.rb) to convert the output to a png file.
 
-```<!---sh-->
+``` <!---sh-->
     ./main Hello | ruby tool.rb > hello.png
 
     $ zbarimg -q hello.png