convert markdown copyright TAB chars into SPACE chars

While not strictly necessary, replacing the two ASCII tab characters
in the markdown copyright comment makes it easier to detect problematic
TAB indentation within markdown files.

After this commit, only 90 markdown files have leading ASCII TAB
characters.  And again, while not strictly necessary, we can consider
running expand on those 90 markdown files to see what effect that
might have on the HTML files they produce.

Replace leading ASCII TAB characters with multiples of 8 ASCII SPACE
characters (the default action of the `expand(1)` tool) might have
an negative effect on some HTML formatting where **hack-a-round**
formatting was attempted to fix broken indentation caused by
problematic ASCII TAB characters.

Think of this as a baseline for evaluating leading
TAB characters within markdown files.

TODO: Consider either using `expand(1)` to replace leading ASCII
TAB characters with multiples of 8 ASCII SPACE characters AND/OR
modifying the appropriate `bin` tool to convert leading ASCII TAB
characters into multiples of 8 ASCII SPACE characters.

1990/westley/index.html

@@ -511,11 +511,11 @@ Jump to: <a href="#">top</a>
 
     You are free to share and adapt this file under the terms of this license:
 
-	Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
+        Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
 
     For more information, see:
 
-	https://creativecommons.org/licenses/by-sa/4.0/
+        https://creativecommons.org/licenses/by-sa/4.0/
 
 -->