This moves the lammps.get_neighlist() method to lammps.numpy.get_neighlist().
lammps.get_neighlist() now returns a NeighList object, while the NumPy variants
returns a NumPyNeighList object. The main difference between the two is that while
the ctypes variant returns neighlist elements as
atom idx (int), numneighs (int), neighbors (POINTER(c_int))
the NumPy variant returns
atom idx (int), neighbors (numpy.array)