Expand all leading tabs in markdown files

Given how problematic leading tabs in markdown files can be,
we have expanded all leading tabs in markdown files by:

```sh
find * -type f -name '*.md' -print |
  while read -r file; do
    rm -f "$file.tmp" ;
    expand < "$file" > "$file.tmp" ;
    mv -f -v "$file.tmp" "$file" ;
  done
```

Given the previous changes to `bin/pandoc-wrapper.sh` and other recent
commits and recent pull requests, the were were **NO** changes to
any HTML files.  This is a **good thing** as the expression goes.

No there are no leading tabs in any markdown files.
A check to catch any re-introduction of leading tabs
into any markdown file is on the way.

BTW: We do not have anything against leading tabs in files,
even though we have had to deal with their impact on forming
HTML from markdown files (as well as the calc source code).
It is just that this is one of those cases where tabs conflict
(sometimes caused by people wanting to change the classic
8-space tab model) with a desired outcome.

Perform `make www` to perform the above and test under macOS.

2020/ferguson1/gameplay.md

@@ -24,7 +24,7 @@ for the input keys.
     *   [**Photosensitive epilepsy/Stimulation overload trigger warnings**](#warning)
     *   [Drawing / Practice mode](#drawing)
     *   [Computer playing / Automatic mode (Photosensitive epilepsy/Stimulation overload trigger)](#auto)
-	    *	[Variations](#auto-variations)
+            *   [Variations](#auto-variations)
     *   [Grow-Shrink (Positive/Negative Winning) mode](#grow-shrink)
     *   [Hypnotic / Sleepy mode (Photosensitive epilepsy/Stimulation overload trigger)](#hypnotic)
     *   [Stimulation / Calming mode](#stim)
@@ -32,16 +32,16 @@ for the input keys.
 
 5.  [Scripts](#scripts)
 
-    *	[Colours selection](#colours)
-    *	[Automate the above gameplay modes](#preset)
+    *   [Colours selection](#colours)
+    *   [Automate the above gameplay modes](#preset)
 
 
 6.  [Other game variables](#variables)
 
-    * [WAIT		    -	Snake speed](#wait)
-    * [EVADE		    -	Bug evasion frequency](#evade)
-    * [SIZE / MAXSIZE	    -	Initial snake / max sizes](#sizes)
-    * [GROW / SHEDS	    -	Growth / Shedding sizes](#growth)
+    * [WAIT                 -   Snake speed](#wait)
+    * [EVADE                -   Bug evasion frequency](#evade)
+    * [SIZE / MAXSIZE       -   Initial snake / max sizes](#sizes)
+    * [GROW / SHEDS         -   Growth / Shedding sizes](#growth)
 
 
 7.  [Conclusion (and inspirational words for everyone)](#conclusions)
@@ -562,11 +562,11 @@ diagonal movement and I also made a mistake and had to modify what I was aiming
 for. But you can consider this mode drawing or practice mode.
 
 ```
-		   oooooooooo   ooooo    o  oo  ooooo
-		   o     o  oo  o   oo   o ooo  o
-		   oooo  o   oo ooooooo  oooo   ooooo
-		      o  o    ooo     oo o ooo  o
-		   oooo  o     oo      ooo  oooooooo>
+                   oooooooooo   ooooo    o  oo  ooooo
+                   o     o  oo  o   oo   o ooo  o
+                   oooo  o   oo ooooooo  oooo   ooooo
+                      o  o    ooo     oo o ooo  o
+                   oooo  o     oo      ooo  oooooooo>
 ```