update unicode ent to reference latest version

Also add example of referencing a specific version.

xep.ent

@@ -393,7 +393,8 @@ THE SOFTWARE.
 <!ENTITY rhttp "<span class='ref'><link url='http://tools.ietf.org/html/draft-lentczner-rhttp'>Reverse HTTP</link></span> <note>Reverse HTTP &lt;<link url='http://tools.ietf.org/html/draft-lentczner-rhttp'>http://tools.ietf.org/html/draft-lentczner-rhttp</link>&gt;.</note>" >
 <!ENTITY rtf "<span class='ref'><link url='http://msdn.microsoft.com/library/en-us/dnrtfspec/html/rtfspec.asp'>Rich Text Format (RTF)</link></span> <note>Rich Text Format (RTF) Version 1.5 Specification &lt;<link url='http://msdn.microsoft.com/library/en-us/dnrtfspec/html/rtfspec.asp'>http://msdn.microsoft.com/library/en-us/dnrtfspec/html/rtfspec.asp</link>&gt;.</note>" >
 <!ENTITY SDN.801c "<span class='ref'>SDN.801c</span> <note>SDN.801c: Access Control Concept and Mechanism, US National Security Agency, Revision C, 12 May 1999.</note>" >
-<!ENTITY unicode "<span class='ref'>Unicode</span> <note>The Unicode Standard, Version 3.2.0 (The Unicode Consortium, 2000).</note>" >
+<!ENTITY unicode "<span class='ref'>Unicode</span> <note>The Unicode Standard, The Unicode Consortium &lt;<link url='http://www.unicode.org/versions/latest/'>http://www.unicode.org/versions/latest/</link>&gt;.</note>" >
+<!ENTITY unicode10 "<span class='ref'>Unicode 10.0.0</span> <note>The Unicode Consortium. The Unicode Standard, Version 10.0.0, (Mountain View, CA: The Unicode Consortium, 2017. ISBN 978-1-936213-16-0) &lt;<link url='https://www.unicode.org/versions/Unicode10.0.0/'>https://www.unicode.org/versions/Unicode10.0.0/</link>&gt;.</note>" >
 <!ENTITY wap "<span class='ref'><link url='http://www.wapforum.org/'>Wireless Access Protocol (WAP)</link></span> <note>Wireless Access Protocol (WAP) &lt;<link url='http://www.wapforum.org/'>http://www.wapforum.org/</link>&gt;.</note>" >
 <!ENTITY wv-csp "<span class='ref'><link url='http://www.openmobilealliance.org/tech/affiliates/wv/wvindex.html'>WV Client-Server Protocol v1.1</link></span> <note>Wireless Village Client-Server Protocol v1.1 &lt;<link url='http://www.openmobilealliance.org/tech/affiliates/wv/wvindex.html'>http://www.openmobilealliance.org/tech/affiliates/wv/wvindex.html</link>&gt;.</note>" >
 <!ENTITY xfn "<span class='ref'><link url='http://gmpg.org/xfn/index'>XHTML Friends Network (XFN)</link></span> <note>XHTML Friends Network (XFN) &lt;<link url='http://gmpg.org/xfn/index'>http://gmpg.org/xfn/index</link>&gt;.</note>" >