Psifr: Analysis and visualization of free recall data

This version adds support for block lag CRP analysis, which measures lags between blocks of serial positions. It also improves the flexibility and consistency of some utilities.

• Support and unit tests for block lag CRP analysis.
• Support for changing the lag field in lag-CRP analysis and determining whether counted possible transitions are transition-unique or not.
• Change to list splitting for better consistency. Now item queries are applied to both study and recall events instead of just study events, except in the context of a transition analysis.
• Added documentation on item and transition filtering.