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.

bin/README.md

@@ -37,7 +37,7 @@ see what is going on with the
 
 
 ``` <!---sh-->
-	bin/quick-readme2index.sh -v 3
+        bin/quick-readme2index.sh -v 3
 ```
 
 to set the verbosity level to `3`. The default for verbosity is `0`, no
@@ -51,7 +51,7 @@ For instance to see what version the [chk-entry.sh](index.html#chk-entry) tool
 is, you would do:
 
 ``` <!---sh-->
-	bin/chk-entry.sh -V
+        bin/chk-entry.sh -V
 ```
 
 
@@ -399,8 +399,8 @@ Baggins](https://www.glyphweb.com/arda/b/bilbobaggins.html)' famous words:
 
 
 ```
-	"Never laugh at live dragons, Bilbo you fool!" he said to himself, and it
-	became a favourite saying of his later, and passed into a proverb.
+        "Never laugh at live dragons, Bilbo you fool!" he said to himself, and it
+        became a favourite saying of his later, and passed into a proverb.
 ```
 
 
@@ -480,11 +480,11 @@ this command will only briefly pause while the
 Usage:
 
 ``` <!---sh-->
-	# For all entries:
+        # For all entries:
     bin/all-run.sh -v 3 bin/quick-readme2index.sh -v 1
 
-	# For an individual entry:
-	bin/quick-readme2index.sh -v 1 2020/ferguson2
+        # For an individual entry:
+        bin/quick-readme2index.sh -v 1 2020/ferguson2
 ```
 
 **NOTE**: This command assumes that the relative
@@ -1222,22 +1222,22 @@ instance, [2020/.year](%%REPO_URL%%/2020/.year) lists, one directory per line,
 the directories of the winning entries of that year. For instance, for 2020:
 
 ``` <!--sh-->
-	$ cat 2020/.year
-	2020/burton
-	2020/carlini
-	2020/endoh1
-	2020/endoh2
-	2020/endoh3
-	2020/ferguson1
-	2020/ferguson2
-	2020/giles
-	2020/kurdyukov1
-	2020/kurdyukov2
-	2020/kurdyukov3
-	2020/kurdyukov4
-	2020/otterness
-	2020/tsoj
-	2020/yang
+        $ cat 2020/.year
+        2020/burton
+        2020/carlini
+        2020/endoh1
+        2020/endoh2
+        2020/endoh3
+        2020/ferguson1
+        2020/ferguson2
+        2020/giles
+        2020/kurdyukov1
+        2020/kurdyukov2
+        2020/kurdyukov3
+        2020/kurdyukov4
+        2020/otterness
+        2020/tsoj
+        2020/yang
 ```