doc: Clean up bibliography rendering for XSLT

In the DSSSL stylesheets, we had an extensive customization of the
bibliography rendering.  Since the bibliography isn't that used much, it
doesn't seem worth doing an elaborate porting of that to XSLT.  So this
just moves some things around, removes some unused things, and does some
minimal XSLT stylesheet customizations to make things look clean.

doc/src/sgml/stylesheet.xsl

@@ -40,6 +40,27 @@
   <xsl:call-template name="inline.monoseq"/>
 </xsl:template>
 
+<xsl:template match="confgroup" mode="bibliography.mode">
+  <span>
+    <xsl:call-template name="common.html.attributes"/>
+    <xsl:call-template name="id.attribute"/>
+    <xsl:apply-templates select="conftitle/text()" mode="bibliography.mode"/>
+    <xsl:text>, </xsl:text>
+    <xsl:apply-templates select="confdates/text()" mode="bibliography.mode"/>
+    <xsl:copy-of select="$biblioentry.item.separator"/>
+  </span>
+</xsl:template>
+
+<xsl:template match="isbn" mode="bibliography.mode">
+  <span>
+    <xsl:call-template name="common.html.attributes"/>
+    <xsl:call-template name="id.attribute"/>
+    <xsl:text>ISBN </xsl:text>
+    <xsl:apply-templates mode="bibliography.mode"/>
+    <xsl:copy-of select="$biblioentry.item.separator"/>
+  </span>
+</xsl:template>
+
 
 <!-- table of contents configuration -->