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/HACKING.md

@@ -29,7 +29,7 @@ snake's syllabary) for all snake and herpetologist programmers alike.
 * Modifications
 
     - Modifying the colours
-	- Background colour
+        - Background colour
     - Modifying the characters for the wall, bug and snake
     - Modifying input keys
     - Modifying the status/score line
@@ -40,7 +40,7 @@ snake's syllabary) for all snake and herpetologist programmers alike.
     - Health (and/or Lives)
     - Saving the game
     - Different types of walls
-	- Blockades
+        - Blockades
     - Diagonal movement
     - Special abilities
     - Obstacles
@@ -228,27 +228,27 @@ More generally the following expressions and data types (with format specifiers)
 come to mind as information that might be of interest.
 
 ```
-    DESCRIPTION		    EXPRESSION		TYPE	FORMAT SPECIFIER
+    DESCRIPTION             EXPRESSION          TYPE    FORMAT SPECIFIER
 
-    Snake size		    A			size_t		%zu
+    Snake size              A                   size_t          %zu
 
-    Y coordinate	    Y			int		%d
+    Y coordinate            Y                   int             %d
     of snake head
 
-    X coordinate	    X			int		%d
+    X coordinate            X                   int             %d
     of snake head
 
-    Max snake size	    g			size_t		%zu
+    Max snake size          g                   size_t          %zu
 
-    Bugs eaten		    c			size_t		%zu
+    Bugs eaten              c                   size_t          %zu
 
-    Bug line (Y)	    *U			int		%d
+    Bug line (Y)            *U                  int             %d
 
-    Bug column (X)	    *V			int		%d
+    Bug column (X)          *V                  int             %d
 
-    Snake size		    A			size_t		%zu
+    Snake size              A                   size_t          %zu
 
-    Growth size (per	    N			size_t		%zu
+    Growth size (per        N                   size_t          %zu
     bug)
 ```
 
@@ -398,10 +398,10 @@ coordinates. This of course is very different now but the idea remains the same:
 ``` <!---c-->
     if (p && !(*O>=O[1]||H>=M(1)))
     {
-	if (X<1||X>=H)
-	    X = X<1?H-1:1;
-	if (Y<2||Y>=*O)
-	    Y = Y<2?*O-1:2;
+        if (X<1||X>=H)
+            X = X<1?H-1:1;
+        if (Y<2||Y>=*O)
+            Y = Y<2?*O-1:2;
     }
 ```