This version adds a system for managing general configuration variables and adds experimental support for filtering recalls using a mechanism similar to the CMR2 model.
Summary of changes:
* Parameter definitions now have support for general configuration variables. These are intended for settings that cause categorical shifts in model behavior, as opposed to graded changes that are specified using standard parameters.
* Support for changing the allowed scope of recall in CMR simulations. The scope, which may be either `list` or `pool`, determines which items are represented in the network and may compete for recall.
* Draft support in CMR for an optional recall filtering mechanism. The context associated with each candidate item is compared to the current state of context. The level of context match determines the probability of a recall being judged as matching.
* Likelihood evaluation now returns statistics for each subject separately within a DataFrame.