Benchmark tests on a random digraph (n = 100000, m = 1000000)

ListDigraph - Building                  0.317446
ListDigraph (sorted arcs) - Building    0.234481
SmartDigraph - Building                 0.121462
SmartDigraph (sorted arcs) - Building   0.107255

ListDigraph - Iteration
  NodeIt:    0.000775194    	0.000766397
  ArcIt:     0.0863013    	0.0863409
  OutArcIt:  0.0817393
  InArcIt:   0.0817207

ListDigraph (sorted arcs) - Iteration
  NodeIt:    0.000770903    	0.000765896
  ArcIt:     0.0120258    	0.0120596
  OutArcIt:  0.0117606
  InArcIt:   0.0775946

SmartDigraph - Iteration
  NodeIt:    9.07183e-05    	9.10997e-05
  ArcIt:     0.000905609    	0.000905704
  OutArcIt:  0.0796823
  InArcIt:   0.0794297

SmartDigraph (sorted arcs) - Iteration
  NodeIt:    9.07898e-05    	9.06944e-05
  ArcIt:     0.000906301    	0.00090549
  OutArcIt:  0.00849271
  InArcIt:   0.0751174