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.

2018/ferguson/FILES.md

@@ -3,9 +3,9 @@
 - [prog.c](prog.c)
     *   This is the source file to the `weasel` program [1].
 - [prog.alt.c](prog.alt.c)
-    *	This is the source code file to the `weasel.alt` program [1].
+    *   This is the source code file to the `weasel.alt` program [1].
 - [test.sh](test.sh)
-    *	Script provided to test the weasel program [1].
+    *   Script provided to test the weasel program [1].
 - [test-strings.txt](test-strings.txt)
     * The `test.sh` script reads from this file and runs the program with these
     target strings.
@@ -47,18 +47,18 @@ remarks I have kept it in place. Please note that the paths below are dependent
 on the prefix used in installation; where I suggest `/usr` it is equally
 possible it could be under '/usr/local', for example.
 
-[1]			    Note that [prog.c](prog.c) and
-			    [prog.alt.c](prog.alt.c) would be
-			    linked to `weasel.c` and `weasel.alt.c`
-			    (respectively) in the `/usr/src/weasel`
-			    subdirectory.
+[1]                         Note that [prog.c](prog.c) and
+                            [prog.alt.c](prog.alt.c) would be
+                            linked to `weasel.c` and `weasel.alt.c`
+                            (respectively) in the `/usr/src/weasel`
+                            subdirectory.
 
-[2]			    The file would most likely be compressed as
-			    `weasel.1.gz` under the `/usr/share/man/man1`
-			    subdirectory.
+[2]                         The file would most likely be compressed as
+                            `weasel.1.gz` under the `/usr/share/man/man1`
+                            subdirectory.
 
-[3]			    These files would be in the `/usr/share/doc/weasel`
-			    subdirectory.
+[3]                         These files would be in the `/usr/share/doc/weasel`
+                            subdirectory.
 
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