other cython modules can now use array_wrap_np
add cython function to convert pele::Array into numpy array
remove parallel connect rountines

It's better to do the whole double ended connect in parallel using
pele.concurrant
started neighbor_iterator class implementation
cell list reset function added
added compare neighbours function
added are_neighbors function and build cell neighbor list function
corrected arguments to AASiteType in pele/angleaxis/aatopology.py
saved symmetry operations as angle-axis rotations as well as matrices in pele/angleaxis/rigidbody.py
implemented cell list next function
added MolecularCluster cluster class and associated minperdist classes/routines
minor reformatting
add some comments
started build atom neighbors list
added simple water cluster test
added virtual destructor
added fortran cell_lists file to use as template
Merge branch 'master' of https://github.com/pele-python/pele into cell_lists
Merge branch 'cell_lists' of https://github.com/smcantab/pele into cell_lists
completed neighbor_iterator, made compilable, needs to be tested