`elections.dtree` v2.0.0

Rewrote the package to use prefio for handling ballots.
Added the function social_choice for computing election results explicitly.
Improved documentation.

`R CMD check` results

GH Actions (via usethis::use_github_action_check_standard()):

✅ macOS (12.6.8 21G725), R==4.3.1
✅ Windows Server (2022 10.0.20348), R==4.3.1-win
✅ Ubuntu (20.04.3), R==4.2.3
✅ Ubuntu (20.04.3), R==4.3.1
✅ Ubuntu (20.04.3), R==devel

0 errors ✔ | 0 warnings ✔ | 0 notes ✔

Other Rhub checks:

✅ debian-clang-devel