Add the pageref element

This instruction is useful if you want to get the number of the page
containing a specific bookmark.

src/file/paragraph/links/pageref-properties.ts

@@ -0,0 +1,16 @@
+// Options according to https://www.ecma-international.org/publications/standards/Ecma-376.htm (at Part 1, Page 1234)
+
+export interface IPageRefOptions {
+    /**
+     * \h option - Creates a hyperlink to the bookmarked paragraph.
+     */
+    readonly hyperlink?: boolean;
+    /**
+     * \p option - Causes the field to display its position relative to the source
+     *  bookmark. If the PAGEREF field is on the same page as the
+     *  bookmark, it omits "on page #" and returns "above" or "below"
+     *  only. If the PAGEREF field is not on the same page as the
+     *  bookmark, the string "on page #" is used.
+     */
+    readonly useRelativePosition?: boolean;
+}