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.

2001/ollinger/README.md

@@ -78,12 +78,12 @@ A: Yes, there are types of entries that show up over and over again.
 
     generating small primes (below is the list of all prime related entries)
 
-	    1985/august
-	    1988/applin
-	    1994/weisberg
-	    1995/makarios
-	    1996/dalbec
-	    2000/bellard
+            1985/august
+            1988/applin
+            1994/weisberg
+            1995/makarios
+            1996/dalbec
+            2000/bellard
 
     As you can see, just a list of primes (let alone small primes)
     does not cut it anymore.
@@ -92,8 +92,8 @@ A: Yes, there are types of entries that show up over and over again.
 
     entries that use some complex state machine/table to print something
 
-	      1988/isaak
-	      1988/phillipps
+              1988/isaak
+              1988/phillipps
 
     Unbeaten for 12 years and counting...
 ```