Fix web site encoding problems

The encoding.html page was generated incorectly, revamp the input
xml.html and convert the full XSLT chain to use and serve it as
UTF-8
* doc/*: fix xml.html, update all stylesheets and regenerate
diff --git a/doc/site.xsl b/doc/site.xsl
index 6f990f3..934d591 100644
--- a/doc/site.xsl
+++ b/doc/site.xsl
@@ -1,6 +1,6 @@
 <?xml version="1.0"?>
 <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
-  <xsl:output method="xml" encoding="ISO-8859-1" indent="yes"
+  <xsl:output method="xml" encoding="UTF-8" indent="yes"
       doctype-public="-//W3C//DTD XHTML 1.0 Transitional//EN"
       doctype-system="http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"/>
 
@@ -606,7 +606,7 @@
     <xsl:variable name="title">
       <xsl:value-of select="$header"/>
     </xsl:variable>
-    <xsl:document href="{$filename}" method="xml" encoding="ISO-8859-1"
+    <xsl:document href="{$filename}" method="xml" encoding="UTF-8"
       doctype-public="-//W3C//DTD XHTML 1.0 Transitional//EN"
       doctype-system="http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
       <html>