Add option for progress visualization

[quietlychris]

I was recently working on some documentation of the DBSCAN algorithm, and on several occasions was running a test on datasets of varying lengths. Even with some very small changes in the parameters, the execution time could jump from under one second to several minutes. While checking progress is not possible for all algorithms, there are at least a few where displaying a progress indicator could be helpful to users for estimating remaining execution time or at least understanding how far along their run is. Obviously, not all users might be interested in this, so making this feature optional with a feature flag might make sense as well.

Options for this could potentially be the indicatif or pb libraries.

[quietlychris]

It looks like the initial issue with long unbounded execution times for DBSCAN was fixed in #100, so I'm putting this on the backburner for the time being