Fixed the examples' documentation and the way the initially print the problem info.

- The biobjective_shortest_path_example and
  tripleobjective_shortest_path_example namespace did not show up in the
  documentation because I had forgotten to add a doxygen comment for it.
- Also started using Doxygen's \addtogroup command instead of \weakgroup
  to add elements to a documentation group (module). (and \defgroup to
  create groups)
- Each example prints some info about the problem before trying to solve it.
  All the info was hardcoded but I made it dynamic.
  (using variables like numVertices, numEdges e.t.c.)