Numerous documentation and test code fixes for HTML Purifier loading

- Improve documentation for stub files
- Synchronize stub files between extras/ and library/
- Remove unnecessary include in function file
- Remove special treatment of Bootstrap
- Improve docs for HTMLPurifier, converted singleton to use static member variables and removed reference
- Add HTMLPurifier.path.php stub file
- Update sample test settings
- Reorganize includes in test files

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1559 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier.path.php

@@ -0,0 +1,9 @@
+<?php
+
+/**
+ * @file
+ * Convenience stub file that adds HTML Purifier's library file to the path
+ * without any other side-effects.
+ */
+
+set_include_path(dirname(__FILE__) . PATH_SEPARATOR . get_include_path() );