prefio 0.2.0

🎉🥳 Made prefio tidy! 🎊🎆
Added a cool new hex sticker!
Reimplemented preferences using vctrs.
Implemented methods required for dplyr operations.
Added a suite of tools for operating on preferences.
Added two summary functions for preferences:
1. instant-runoff voting algorithm
2. covariance matrix based on rankings matrix representation
Improved preflib interface to fail gracefully, which is why prefio 0.1.1 was taken down from CRAN.

prefio 0.1.1

Changed string formatting for preferences (now displays as [A > B > C] rather than "A > B > C").
Fixed a bug when loading preferences from orderings format.
Allows an empty preferences object (displays preferences(0)).
Allow blank preferences (displays [blank]).