Added a basic IP algorithm.  It's 10x faster than James' IP_with_timing.  Needs a bit more work such as a return_results method and docstrings.
Updated docstring in tortuosity
find_neighbor_pores and _throats were sending back ndarrays most of the time, but empty lists [ ] when no neighbors were found.  This was breaking things so I forced arrays.
Fixed bug #254: There were several places using if pores != [ ] that were changed to pores is not [ ]
Fixed bug #242: During the _labels method, arrays were being made based on the size of pores, which worked great when pores was indices, but when pores were a mask, the size was always Np.  This now converts to indices first.
Tiny change to _get_indices so that always returns an int32 array.  For some reason, sp.where returns an int64 array.
Adding plot_primary_drainage_curve in the Petroleum Eng. style. Also change the units of the pore and throat diameters distribution to [micro-m]. The current [m] units is too big for the simulations we are doing.
Merge branch 'develop' of https://github.com/PMEAL/OpenPNM into develop
Clean-ups of labels and _get_labels.  Some Numpy functions return int32 and other int64.  Also, for some reason pores == [ ] works and pores is not [ ] works, but pores is [ ] fails and pores != [ ] fails.
Playing with the __new__ method
- Added a __new__ that creates all the default attributes (_net, etc)
- Added a _load class_method that returns an instance by calling the __new__ method, so we get an instance without requiring default arguments
- The _load method also fills the instances dictionary
- Also needed to attach the logger during the _load command, so I created an _add_logger method that does so.  This is called by __init__, but also by _load.
Minor mods to plotting functions
Getting rid of versioneer
Merge branch 'develop' of https://github.com/PMEAL/OpenPNM into develop

Conflicts:
	OpenPNM/Postprocessing/Plots.py
Comment out logger calls, allow conduit_lengths to work without centroids by defaulting to pore coordinates