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.

1990/jaw/README.md

@@ -180,8 +180,8 @@ with one shell cmd at the far end.
     p=0
     for f in `ls /tmp/shark$$*`
     do
-	 p=`expr $p + 1`
-	 mail -s "bundle ($p of $n) from '`whoami`'" $m < $f
+         p=`expr $p + 1`
+         mail -s "bundle ($p of $n) from '`whoami`'" $m < $f
     done
     rm /tmp/shark$$*
 ```
@@ -190,33 +190,33 @@ with one shell cmd at the far end.
 ### Shark history:
 
 - May 1987: Karl Fox introduces 1023-byte `zcat.c` to USENET.
-	     It's too late for the 4th IOCCC.
+             It's too late for the 4th IOCCC.
 
 - May 21, 1987: James A. Woods extends idea to construct self
-	     decompressing `shar` Trojan horse, utilizing `cc`, `shar`,
-	     `zcat`, & `btoa`; size: 2303 bytes.
+             decompressing `shar` Trojan horse, utilizing `cc`, `shar`,
+             `zcat`, & `btoa`; size: 2303 bytes.
 
 - May 23, 1987: `jaw` trims 250 bytes without much thought.
 
 - June 2, 1987: 52 lines of shell, 1991 bytes, now made with `tar`,
-	     short-circuit C-compile at far end, dual-use main.c,
-	     portability mods. (jaw)
+             short-circuit C-compile at far end, dual-use main.c,
+             portability mods. (jaw)
 
 - Mar-May 1988: abortive run at 5th IOCCC.
-	     `jaw.c` - 1529 bytes. compile line: 152 bytes.
-	     generated funny code with `execvp()` to invoke shell.
+             `jaw.c` - 1529 bytes. compile line: 152 bytes.
+             generated funny code with `execvp()` to invoke shell.
 
 - Aug 29, 1988: production version, now at 1830 bytes.
 
 - Jan 1990: Paul Eggert does tour-de-force shark re-engineering.
 
 - May 24, 1990: collaboration yields 999-byte `jaw.c` core (see above)
-	     and 1530-byte production shell code (w/comments).
-	     Eggert comes through with lion's share of improvements.
-	     7th IOCCC code now faster than the `btoa`/`zcat` it replaces.
+             and 1530-byte production shell code (w/comments).
+             Eggert comes through with lion's share of improvements.
+             7th IOCCC code now faster than the `btoa`/`zcat` it replaces.
 
 - May 1990: `jaw` develops experimental replacement using
-	     Dan Bernstein's high-compression 'squeeze'.
+             Dan Bernstein's high-compression 'squeeze'.
 
 
 To which we add: