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/ferguson2/recode.md

@@ -9,9 +9,9 @@ have to if you don't wish to.
 <div id="toc">
 -   [What is recode and why is it recommended?](#recode)
 -   [Options](#options)
-    *	[Protecting against the same I/O file](#samefile)
-    *	[File options parser limitation](#fileoptions)
-    *	[`-R` option validation?](#validation)
+    *   [Protecting against the same I/O file](#samefile)
+    *   [File options parser limitation](#fileoptions)
+    *   [`-R` option validation?](#validation)
 -   [Piping commands to recode](#pipingtorecode)
 -   [Piping recode to the Enigma simulator](#pipingtoenigma)
 -   [Manually test the recode program with the Enigma program](#manuallytest)
@@ -63,11 +63,11 @@ wonderful 'challenge' for everyone.
 ``` <!---sh-->
     ./recode -h
     usage: ./recode [options]
-    -v			display selected settings
-    -r			pseudo-randomly select settings
-    -f<input file>	read file for Enigma input
-    -R<string|file>	init settings from settings string or file
-    -o<output file>	write settings to file
+    -v                  display selected settings
+    -r                  pseudo-randomly select settings
+    -f<input file>      read file for Enigma input
+    -R<string|file>     init settings from settings string or file
+    -o<output file>     write settings to file
 ```