Add changelog and release note for #587

ChangeLog

@@ -6,6 +6,9 @@
 	the last string returned. This is necessary in order to fully
 	retrieve values of strings that may contain embedded null characters.
 
+	* C API: Add qpdf_oh_new_object to clone an object handle. Change
+	implemented by m-holger in #587.
+
 2021-11-16  Jay Berkenbilt  <ejb@ql.org>
 
 	* 10.4.0: release

manual/qpdf-manual.xml

@@ -5140,6 +5140,12 @@ print "\n";
           from the C API, you still have to be able to detect them.
          </para>
         </listitem>
+        <listitem>
+         <para>
+          Add <function>qpdf_oh_new_object</function> to the
+          C API. This allows you to clone an object handle.
+         </para>
+        </listitem>
        </itemizedlist>
       </listitem>
      </itemizedlist>