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/URI.Base.txt

@@ -0,0 +1,17 @@
+URI.Base
+TYPE: string/null
+VERSION: 2.1.0
+DEFAULT: NULL
+--DESCRIPTION--
+
+<p>
+    The base URI is the URI of the document this purified HTML will be
+    inserted into.  This information is important if HTML Purifier needs
+    to calculate absolute URIs from relative URIs, such as when %URI.MakeAbsolute
+    is on.  You may use a non-absolute URI for this value, but behavior
+    may vary (%URI.MakeAbsolute deals nicely with both absolute and
+    relative paths, but forwards-compatibility is not guaranteed).
+    <strong>Warning:</strong> If set, the scheme on this URI
+    overrides the one specified by %URI.DefaultScheme.
+</p>
+--# vim: et sw=4 sts=4