Renaming variables for consistency with C++ library

[apulsipher]

This PR brings renaming changes to bring the R package in line with the C++ library.

It also adds several getters that were on the C++ side, but not implemented in R until now.

Finally, it adds a fourth version number in the DESCRIPTION file to track patches on the R package that aren't correlated to updates on the C++ library.

[codecov]

Codecov Report

Attention: Patch coverage is 94.89796% with 5 lines in your changes missing coverage. Please review.

Project coverage is 38.72%. Comparing base (6c3beac) to head (d2d6ca0).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lfmcmc.cpp	94.23%	3 Missing ⚠️
R/LFMCMC.R	95.65%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #66      +/-   ##
==========================================
+ Coverage   36.61%   38.72%   +2.11%     
==========================================
  Files          36       36              
  Lines        1991     2058      +67     
==========================================
+ Hits          729      797      +68     
+ Misses       1262     1261       -1     

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[gvegayon]

Almost there!

[apulsipher]

@gvegayon Made the requested changes and brought in the latest from C++ library. Is this okay to merge?