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.

tmp/OLD_manifest/README.md

@@ -489,10 +489,10 @@ following fields:
 
    This field indicates if the file main program.  This filed is one of:
 
-   main		The main source code to display.
-   alt		The alternative source code.
-   orig		The original version of the source code (may be the same as main).
-   null		Not a primary, nor alternative, nor original source code file.
+   main         The main source code to display.
+   alt          The alternative source code.
+   orig         The original version of the source code (may be the same as main).
+   null         Not a primary, nor alternative, nor original source code file.
 
 7. filetype:
 
@@ -516,14 +516,14 @@ following fields:
    A string indicating how the file is to be displayed from `winners.html`.
    Possible files include:
 
-   browser	The file is to be displayed directly from the browser.
-   github	The file should be linked to the GitHub repo so that
-		it may be rendered directly by GitHub.  In the future
-		this may changed to allow a suitable browser to
-		directly display this file instead of via GitHub.
-   download	The file is intended to be downloaded from the browser
-		instead of being displayed.
-   null		This file not listed in `winners.html`.
+   browser      The file is to be displayed directly from the browser.
+   github       The file should be linked to the GitHub repo so that
+                it may be rendered directly by GitHub.  In the future
+                this may changed to allow a suitable browser to
+                directly display this file instead of via GitHub.
+   download     The file is intended to be downloaded from the browser
+                instead of being displayed.
+   null         This file not listed in `winners.html`.
 
    NOTE: When display_via is null, winners_show MUST be false.