Implement *neighbor_list* ASE function for the bond length analysis example

[blokhin]

via Jinhyun Chang:

In your example script for bond length analysis using ASE: it is mentioned that ASE is slow, and you could use a C-extension to speed it up. However, it looks like the algorithm for carrying out the bond length analysis is the culprit. Using the ASE's neighbor_list function, we found a speed-up of at least a factor of 2 in a similar example. We could not execute this particular example (as mentioned in a previous comment).