DocBook-DTD: Match full docbook DTD as well as simplified

[JPEWdev]

Makes the work "Simplified" optional in the Docbook DTD license so that it will match both the full Docbook DTD license and the Simplified Docbook DTD license.

[xsuchy]

Can you link the source code or the license that uses this variant?

[JPEWdev]

I couldn't find an authorative git archive for a direct link, but it's in this archive: http://www.oasis-open.org/docbook/sgml/4.1/docbk41.zip in the docbook.dtd file.

And copied here for reference:

<!-- Copyright 1992-2000 HaL Computer Systems, Inc.,
     O'Reilly & Associates, Inc., ArborText, Inc., Fujitsu Software
     Corporation, and the Organization for the Advancement of
     Structured Information Standards (OASIS).

     $Id: docbook.dtd,v 1.11 2000/06/19 14:42:02 nwalsh Exp $

     Permission to use, copy, modify and distribute the DocBook DTD and
     its accompanying documentation for any purpose and without fee is
     hereby granted in perpetuity, provided that the above copyright
     notice and this paragraph appear in all copies.  The copyright
     holders make no representation about the suitability of the DTD for
     any purpose.  It is provided "as is" without expressed or implied
     warranty.

     If you modify the DocBook DTD in any way, except for declaring and
     referencing additional sets of general entities and declaring
     additional notations, label your DTD as a variant of DocBook.  See
     the maintenance documentation for more information.

     Please direct all questions, bug reports, or suggestions for 
     changes to the docbook@lists.oasis-open.org mailing list. For more
     information, see http://www.oasis-open.org/docbook/.
-->

[JPEWdev]

Looks like I missed another minor difference, let me fix that...