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.

2012/tromp/README.md

@@ -1,9 +1,9 @@
 ## To build:
 
 ``` <!---sh-->
-    make all		# On a 64-bit machine (default)
+    make all            # On a 64-bit machine (default)
 
-    make tromp32		# On a 32-bit machine
+    make tromp32                # On a 32-bit machine
 ```
 
 
@@ -371,7 +371,7 @@ and change it to BLC8 with
 ``` <!---sh-->
     $ cat deflate.Blc reverse.blc | ./tromp > rev.Blc
     $ wc rev.Blc
-	0 1 9 rev.Blc
+        0 1 9 rev.Blc
 ```
 
 and then try it out with:

2012/tromp/how.md

@@ -38,30 +38,30 @@ free list.
 Here's what each variable does:
 
 ```
-    L	Lambda term space
-    m	mode: 0 for bits and 7 for bytes
-    b	bits remaining unread in I, -1 on EOF
-    D	Desirable temporary
-    c	continuation context
-    a	active environment pointer
-    C	Current term index
-    U	Ultimate term pointer
-    u	utility entry
-    B	Born to be free-list of closures
-    I	Input character
-    O	Output character
-    e	entry of current term
+    L   Lambda term space
+    m   mode: 0 for bits and 7 for bytes
+    b   bits remaining unread in I, -1 on EOF
+    D   Desirable temporary
+    c   continuation context
+    a   active environment pointer
+    C   Current term index
+    U   Ultimate term pointer
+    u   utility entry
+    B   Born to be free-list of closures
+    I   Input character
+    O   Output character
+    e   entry of current term
 ```
 
 Here's what each of the 6 auxiliary functions do:
 
 ```
-    s	variable lookup in active environment with de Bruijn index u
-    S	gets one bit of input, setting b to -1 on EOF or to remaining number of bits in current byte
-    k	copy fragment from string literal holding lambda terms xor 46 into current end of term space
-    x	expand input, adding 11 (resp. 99) entries to term space for bit (resp. byte) mode
-    p	parses BLC-encoded lambda term using S(), stores results in term space and returns length
-    d	decrease reference counter, add record to free list on reaching zero
+    s   variable lookup in active environment with de Bruijn index u
+    S   gets one bit of input, setting b to -1 on EOF or to remaining number of bits in current byte
+    k   copy fragment from string literal holding lambda terms xor 46 into current end of term space
+    x   expand input, adding 11 (resp. 99) entries to term space for bit (resp. byte) mode
+    p   parses BLC-encoded lambda term using S(), stores results in term space and returns length
+    d   decrease reference counter, add record to free list on reaching zero
 ```