uri: Use url.uri.(rfc3986|whatwg) entities

Author: TimWolla

reference/uri/book.xml

@@ -14,9 +14,9 @@
   </simpara>
   <simpara>
    This extension implements functionality that follows the
-   <link xlink:href="http://www.ietf.org/rfc/rfc3986.txt">RFC 3986,
+   <link xlink:href="&url.url.rfc3986;">RFC 3986,
    Uniform Resource Identifier (URI): Generic Syntax</link> and
-   <link xlink:href="https://url.spec.whatwg.org/">WHATWG URL Standard</link>
+   <link xlink:href="&url.url.whatwg-url;">WHATWG URL Standard</link>
    specifications.
   </simpara>
  </preface>