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/blakely/README.md

@@ -1,6 +1,6 @@
 ## To build:
 
-```<!---sh-->
+``` <!---sh-->
     make
 ```
 
@@ -9,20 +9,20 @@
 
 Zoom out and make your terminal window 53 or more lines deep.
 
-```<!---sh-->
+``` <!---sh-->
     ./blakely < blakely.c | head -300
 ```
 
 
 ## Try:
 
-```<!---sh-->
+``` <!---sh-->
     ./try.sh
 ```
 
 For those who have a lot of time, try:
 
-```<!---sh-->
+``` <!---sh-->
     ./blakely < t0_3.dat
 ```
 
@@ -40,7 +40,7 @@ is a [Garden of Eden](http://en.wikipedia.org/wiki/Garden_of_Eden_%28cellular_au
 If you have enough time to spare, put the plan of your garden in a text file,
 and run:
 
-```<!---sh-->
+``` <!---sh-->
     ./blakely - < garden.txt
 ```
 
@@ -54,7 +54,7 @@ over tabs.
 
 In order to see the main feature of the code, type:
 
-```<!---sh-->
+``` <!---sh-->
     ./blakely < blakely.c
 ```
 
@@ -72,7 +72,7 @@ layout of the source-code is such that it evolves to a digital representation of
 the first 15 decimal places of pi after 4 time steps. This was setup using the
 other feature of the program which can be demonstrated as follows:
 
-```<!---sh-->
+``` <!---sh-->
     ./blakely - < 3.dat
 ```
 
@@ -81,7 +81,7 @@ more grids (taking a few minutes to display the last). Waiting for any more
 grids will take a substantial amount of time. The final grid has been put into
 [evolve_to_3.dat](evolve_to_3.dat), and if you type
 
-```<!---sh-->
+``` <!---sh-->
     ./blakely < evolve_to_3.dat
 ```