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.

2011/toledo/README.md

@@ -2,7 +2,7 @@
 
 If you have X11 installed:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
@@ -13,7 +13,7 @@ Windows](toledo.alt2.c). See [Alternate code](#alternate-code) below.
 
 ## To use:
 
-```<!---sh-->
+``` <!---sh-->
     ./toledo
 ```
 
@@ -49,7 +49,7 @@ but you can change them about however you like, even with other keys. For
 instance to swap `LEFT` and `RIGHT`:
 
 
-```<!---sh-->
+``` <!---sh-->
     make clobber LEFT=XK_Right:XK_d RIGHT=XK_Left:XK_a alt
 ```
 
@@ -75,7 +75,7 @@ the source early on, right before the code gets hard to follow, or using the
 Like Oscar's previous winning X11 program for the 19th IOCCC, if
 you remove both the X11 include files and replace them with
 
-```<!---c-->
+``` <!---c-->
     #include "layer.c"
 ```