I do not see a way to see the rank/rating assigned the players at the end of a match?
I'm not altering the PGN headers, just making their key/values searchable. It should be possible though to estimate the Elo rating from the match results.
I only see a win/draw/lose outcome. How do I derive a rating from a binary result?
https://en.wikipedia.org/wiki/Elo_rating_system
Basically is something like this: by looking at the difference between the ratings of the two players you derive the non-binary expected result. The difference between the real and the expected result is then converted to rating gain or loss.
Tools for downloading, parsing, and searching PGN:
https://github.com/josephbharrison/pgn-tools
Merry Christmas everyone!