[1.7.0] Add documentation for the Tidy functionality

- Make specifying the child property for ElementDef unnecessary when overloading content_model or content_model_type
- Add necessary includes to Tidy module files
- Move div@align fix to Tidy_Proprietary
- Future proof attrTransform.php by setting doctype to strict

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1071 48356398-32a2-884e-a903-53898d9a118a

smoketests/attrTransform.php

@@ -42,6 +42,7 @@ $xml = simplexml_load_file('attrTransform.xml');
 
 // attr transform enabled HTML Purifier
 $config = HTMLPurifier_Config::createDefault();
+$config->set('HTML', 'Doctype', 'XHTML 1.0 Strict');
 $purifier = new HTMLPurifier($config);
 
 $title = isset($_GET['title']) ? $_GET['title'] : true;