Add concrete type aliases of VertexMap and EdgeMap for Graph and AppendGraph

src/models/append_graph.rs

@@ -7,6 +7,9 @@ pub struct Vertex(usize);
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub struct Edge(usize);
 
+pub type AppendGraphVertexMap<T> = VertexMap<Vertex, T>;
+pub type AppendGraphEdgeMap<T> = EdgeMap<Edge, T>;
+
 impl Edge {
     fn normalize(&self) -> Self {
         Self(self.0 & !1)