Improve html generation

Set some parameters for the docbook style sheets:
- generate links from man page references
- suppress chapter numbering

doc/xmlto-config.xsl

@@ -3,4 +3,7 @@
                 xmlns:fo="http://www.w3.org/1999/XSL/Format"
                 version="1.0">
   <xsl:param name="html.stylesheet" select="'docbook.css'"/>
+  <xsl:param name="citerefentry.link" select="1"/>
+  <xsl:template name="generate.citerefentry.link"><xsl:text>#</xsl:text><xsl:value-of select="refentrytitle"/></xsl:template>
+  <xsl:param name="chapter.autolabel" select="0"></xsl:param>
 </xsl:stylesheet>