Add GraphTopology::edges() and tests

src/traits.rs

@@ -1,5 +1,4 @@
 // TODO: Add functions to reserve memory for vertices and edges.
-// TODO: Add iterator of all edges.
 // TODO: Add iterator of incident edges for a vertex.
 // TODO: Add finding incident vertices for an edge.
 // TODO: Split out GraphTopologyAddition trait.
@@ -13,6 +12,7 @@ pub trait GraphTopology {
     fn are_adjacent(&self, v1: Self::Vertex, v2: Self::Vertex) -> bool;
     fn vertices(&self) -> impl Iterator<Item = Self::Vertex>;
     fn neighbors(&self, v: Self::Vertex) -> impl Iterator<Item = Self::Vertex>;
+    fn edges(&self) -> impl Iterator<Item = Self::Edge>;
     fn add_vertex(&mut self) -> Self::Vertex;
     fn add_edge(&mut self, v1: Self::Vertex, v2: Self::Vertex) -> Self::Edge;
 }