Log Message:
Update to 1.2.0:
# 1.2.0

    * New algorithm added: Bidirectional Dijkstra's shortest path
    * A lot of bugfixes
    * Revised documentation

# 1.1.0

    * Returned to the libtool versioning style
    * New algorithms added
          o Dijkstra's shortest path
          o Bellman Ford shortest path
          o New variant of Maximal Flow
    * graph::load now creates nodes in the same order as they are in the gml file
    * graph::load now with parameter 'preserve_ids' to use the same ids as in \ 
the gml file
    * A lot of bugfixes
    * Documentation adapted to doxygen

# 1.0.0

    * First stable release
    * quick fix of bug in graph::del_node (thanks to David Auber)
    * bug fix in graph::hide_node (thanks to David Auber)
    * optimization of reallocation procedure in node_ and edge_maps (again, \ 
thanks to David)