Psifr: Analysis and visualization of free recall data

This version adds a new analysis, conditional response probability by input (input-CRP). It also increases the flexibility of plotting, with options to map a facet of the data to line style and an option to more easily include all lags in a lag-CRP plot.

• Add a new analysis, input_crp, and its corresponding statistics function, count_input_pairs. It tracks the response probability of different input positions as a function of the previous input position, conditional on availability.
• Line plot functions now support mapping a facet of the data to line style.
• The plot_lag_crp function will now plot all possible lags if max_lag is set to None.