Fix doxygen warnings

doc/qgis3_user_changes.dox

@@ -4,21 +4,21 @@
 
 Notes regarding user related changes for QGIS 3.0 which should be included in the release notes.
 
-\subsection qgis3_user_changes_expressions Expressions
+\section qgis3_user_changes_expressions Expressions
 
 QGIS 3.0 brings some changes to the expression engine, which may require existing projects to
 be updated so that any expressions in use have the following changes:
 <ul>
-<li>$rownum has been replaced by @row_number</li>
-<li>$scale has been replaced by @map_scale</li>
-<li>$map has been replaced by @map_id</li>
-<li>$numpages has been replaced by @layout_numpages</li>
-<li>$page has been replaced by @layout_page</li>
-<li>$feature has been replaced by @atlas_featurenumber</li>
-<li>$atlasfeatureid has been replaced by @atlas_featureid</li>
-<li>$atlasfeature has been replaced by @atlas_feature</li>
-<li>$atlasgeometry has been replaced by @atlas_geometry</li>
-<li>$numfeatures has been replaced by @atlas_totalfeatures</li>
+<li>$rownum has been replaced by \@row_number</li>
+<li>$scale has been replaced by \@map_scale</li>
+<li>$map has been replaced by \@map_id</li>
+<li>$numpages has been replaced by \@layout_numpages</li>
+<li>$page has been replaced by \@layout_page</li>
+<li>$feature has been replaced by \@atlas_featurenumber</li>
+<li>$atlasfeatureid has been replaced by \@atlas_featureid</li>
+<li>$atlasfeature has been replaced by \@atlas_feature</li>
+<li>$atlasgeometry has been replaced by \@atlas_geometry</li>
+<li>$numfeatures has been replaced by \@atlas_totalfeatures</li>
 </ul>
 
 */