add classified reference manual for Mesh_2

Mesh_2/doc/Mesh_2/PackageDescription.txt

@@ -19,5 +19,24 @@
 \cgalPkgDemo{2D Mesh Generator,constrained_delaunay_triangulation_2.zip}
 \cgalPkgShortInfoEnd
 \cgalPkgDescriptionEnd
-*/
 
+## Concepts ##
+- `ConformingDelaunayTriangulationTraits_2`
+- `DelaunayMeshTraits_2`
+- `MeshingCriteria_2`
+- `DelaunayMeshFaceBase_2`
+
+## Classes##
+- `CGAL::Triangulation_conformer_2<CDT>`
+- `CGAL::Delaunay_mesher_2<CDT, Criteria>`
+- `CGAL::Delaunay_mesh_face_base_2<Traits, Fb>`
+- `CGAL::Delaunay_mesh_criteria_2<CDT>`
+- `CGAL::Delaunay_mesh_size_criteria_2<CDT>`
+- `CGAL::Mesh_2::Face_badness`
+
+## Global functions ##
+- `CGAL::make_conforming_Delaunay_2`
+- `CGAL::make_conforming_Gabriel_2`
+- `CGAL::refine_Delaunay_mesh_2`
+
+*/