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.

1991/ant/README.md

@@ -88,23 +88,23 @@ results depending on the implementation of `curses`.
 ### Commands
 
 ```
-    h j k l	    left, down, up, right cursor movement
-    H J K L	    word left, page down, page up, word right
-    [ ]		    beginning and end of line
-    t b		    top and bottom of file
-    i		    enter insert mode, form-feed to quit
-    x		    delete character under the cursor
-    W		    write buffer to file
-    R		    refresh the screen
-    Q		    quit
+    h j k l         left, down, up, right cursor movement
+    H J K L         word left, page down, page up, word right
+    [ ]             beginning and end of line
+    t b             top and bottom of file
+    i               enter insert mode, form-feed to quit
+    x               delete character under the cursor
+    W               write buffer to file
+    R               refresh the screen
+    Q               quit
 ```
 
 
 ### Exit status
 
 ```
-    0		    success
-    2		    missing edit filename
+    0               success
+    2               missing edit filename
 ```
 
 
@@ -142,24 +142,24 @@ screen with long lines.  Paging up and down should work correctly, however.
 
 ### References:
 
-[Fin80]	Craig A. Finseth, "Theory and Practice of Text Editors or<br>
-	A Cookbook For An EMACS", TM-165, MIT Lab. for Computer<br>
-	Science
+[Fin80] Craig A. Finseth, "Theory and Practice of Text Editors or<br>
+        A Cookbook For An EMACS", TM-165, MIT Lab. for Computer<br>
+        Science
 
-[KeP81]	Kernighan & Plauger, "Software Tools in Pascal",<br>
-	Addison-Wesley, 81, chapter 6
+[KeP81] Kernighan & Plauger, "Software Tools in Pascal",<br>
+        Addison-Wesley, 81, chapter 6
 
-[Mil86]	Eugene W. Myers & Webb Miller, "Row-replacement Algorithms
-	for Screen Editors", TR 86-19, Dept. of Computer Science,<br>
-	U. of Arizona
+[Mil86] Eugene W. Myers & Webb Miller, "Row-replacement Algorithms
+        for Screen Editors", TR 86-19, Dept. of Computer Science,<br>
+        U. of Arizona
 
-[MyM86]	Eugene W. Myers & Webb Miller, "A simple row-replacement<br>
-	method", TR 86-28, Dept. of Computer Science, U. of Arizona
+[MyM86] Eugene W. Myers & Webb Miller, "A simple row-replacement<br>
+        method", TR 86-28, Dept. of Computer Science, U. of Arizona
 
-[Mil87]	Webb Miller, "A Software Tools Sampler", Prentice Hall, 87
-	ISBN 0-13-822305-X, chapter 5
+[Mil87] Webb Miller, "A Software Tools Sampler", Prentice Hall, 87
+        ISBN 0-13-822305-X, chapter 5
 
-[net90]	"Editor 101/102" articles from comp.editors
+[net90] "Editor 101/102" articles from comp.editors
 
 
 <!--