Escape story fields and clean story HTML with HTML Purifier.

Add HTML Purifier 4.19.1. Stories are purified when they are saved and
when they are shown.

lib/htmlpurifier-4.19.1/library/HTMLPurifier/ConfigSchema/schema/HTML.Proprietary.txt

@@ -0,0 +1,12 @@
+HTML.Proprietary
+TYPE: bool
+VERSION: 3.1.0
+DEFAULT: false
+--DESCRIPTION--
+<p>
+    Whether or not to allow proprietary elements and attributes in your
+    documents, as per <code>HTMLPurifier_HTMLModule_Proprietary</code>.
+    <strong>Warning:</strong> This can cause your documents to stop
+    validating!
+</p>
+--# vim: et sw=4 sts=4