graph_to_eps mission accomplished.
- lemon/graph_to_eps.h header created
- lemon/bezier.h: Tools to compute with bezier curves (unclean and undocumented
interface, used internally by graph_to_eps.h)
- demo/graph_to_eps_demo.cc: a simple demo for lemon/graph_to_eps.h

 /*!

 \page developpers_interface Developpers' interface to graph structures

 Under construction

 */