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/burton2/README.md

@@ -137,7 +137,7 @@ The discrepancies found are documented and explained in the file
 
 ``` <!---sh-->
     find ~/src/obc -type f -a -name "*.c" | xargs ./spotcheck.sh ./prog | ./spotdiff.sh |
-	    grep -v keep | diff -bw - discrep* | grep "[<>] cl "
+            grep -v keep | diff -bw - discrep* | grep "[<>] cl "
 ```
 
 In summary, there are only 6 unique entries out of 366 that have any variation
@@ -228,38 +228,38 @@ language_.  It really is this easy with `tac`:
     #!/usr/bin/env bash
     script='
     BEGIN {
-	    last=nl="\n";
-	    f="c11"; while(getline <f > 0) kw[$0]++; close(f);
+            last=nl="\n";
+            f="c11"; while(getline <f > 0) kw[$0]++; close(f);
     }
 
     function iskw(a)   { return a in kw }
     function indent(a) { return sprintf("%*s", n*3, " ") }
     function newline() { if (!infor && last != nl) printf last=nl; }
     function show(a) {
-	    if (last==nl) printf "%s", indent()
-	    printf "%s%s", space(), a
-	    last=a
+            if (last==nl) printf "%s", indent()
+            printf "%s%s", space(), a
+            last=a
     }
     function space() {
-	    return iskw(last) ||
-	      (last ~ /[A-Za-z0-9_+-\/%^[&\]\)=:<>;]$/ && $0 !~ /[:;()\[\],]/) ? " " : ""
+            return iskw(last) ||
+              (last ~ /[A-Za-z0-9_+-\/%^[&\]\)=:<>;]$/ && $0 !~ /[:;()\[\],]/) ? " " : ""
     }
 
-    /^\(/	{ ++paren }
-    /^\)/	{ --paren }
+    /^\(/       { ++paren }
+    /^\)/       { --paren }
 
-    /^for/		    { newline(); infor=1 }
-    infor && /^;/	    { ++infor; show($0 " "); next }
+    /^for/                  { newline(); infor=1 }
+    infor && /^;/           { ++infor; show($0 " "); next }
     infor==1 && /^:/    { ++infor }
     infor>1 && paren==0 { infor=0 }
 
-    /^\?/		{ tern++; n++; newline(); show($0 " "); next }
-    tern && /^:/	{ newline(); show($0); --tern; --n; next }
+    /^\?/               { tern++; n++; newline(); show($0 " "); next }
+    tern && /^:/        { newline(); show($0); --tern; --n; next }
 
-    /^#/	{ newline(); show($0); newline(); next }
-    /^;/	{ show($0); newline(); next }
-    /^{/	{ show($0); ++n; newline(); next }
-    /^}/	{ n--; newline(); show($0); newline(); next }
+    /^#/        { newline(); show($0); newline(); next }
+    /^;/        { show($0); newline(); next }
+    /^{/        { show($0); ++n; newline(); next }
+    /^}/        { n--; newline(); show($0); newline(); next }
 
     { show($0) }
     '
@@ -329,9 +329,9 @@ The following reserved word files are included:
 * [kandr](%%REPO_URL%%/2018/burton2/kandr)    from my venerable 1978 18th printing "The C Programming Language"
 * [v7unix](%%REPO_URL%%/2018/burton2/v7unix)  7th edition Unix source code, extracted from c00.c
 * [kandr2](%%REPO_URL%%/2018/burton2/kandr2)  from my 1988 1st printing "The C Programming Language", 2e
-* [ansi](%%REPO_URL%%/2018/burton2/ansi)	    ANSI X3.159-1989
-* [c99](%%REPO_URL%%/2018/burton2/c99)	    ISO/IEC 9899:1999(E)
-* [c11](%%REPO_URL%%/2018/burton2/c11)	    ISO/IEC 9899:201x(E) N1570
+* [ansi](%%REPO_URL%%/2018/burton2/ansi)            ANSI X3.159-1989
+* [c99](%%REPO_URL%%/2018/burton2/c99)      ISO/IEC 9899:1999(E)
+* [c11](%%REPO_URL%%/2018/burton2/c11)      ISO/IEC 9899:201x(E) N1570
 * [c++98](%%REPO_URL%%/2018/burton2/c++98)    http://en.cppreference.com/w/cpp/keyword
 * [c++11](%%REPO_URL%%/2018/burton2/c++11)    ISO/IEC 14882:2011(E) N3337 2012-01-16
 * [c++14](%%REPO_URL%%/2018/burton2/c++14)    ISO/IEC 14882:2014(E) N4296 2014-11-09