First version of the advanced add_grid_edges
Error checking and minor fixes
Moving towards the new API of NumPy.

Using uintptr_t to store pointers as int.
New NumPy API. Export graph to networkx.
Moore and von Neumann structures. Minor fixes
range -> xrange
Included a solver of stereograms as example of alpha-expansion
Documentation of add_grid_edges
Update to the version 1.2.0 (merge with develop)