Better methods for varying descriptors

[jonlym]

The current code works best for processing two descriptors. Need to set up scenarios for 1D and >2D analysis.

[jonlym]

Would also be useful to support Matplotlib

[jonlym]

Added 1D volcano plots in 1d7d7dc

[jonlym]

Superimposed literature values in 1D volcano plots in 63c15a1