feature request: control C++ from python

[bagrow]

It would be nice to call the speedy-but-limited C++ code directly from link_clustering.py. For example:
python link_clustering.py -f net.pairs

It is not clear to me if this should store the potentially large .jaccs file, or remove it when finished to avoid confusing the user.

[yy]

I think it may be good to have an option like '-c' to use c++ code. I also think we should keep self-contained python version because it may be annoying to compile c++ version to run the program for very simple graphs.

[bagrow]

I think if we do a proper python setup.py install it can compile the C++ files just once and stash them on the user's path so they can be called whenever python link_clustering.py -c is called.