[EM] Median ratings

[Kristofer Munsterhjelm]

Hello,

Is it possible to make Median Ratings summable? Median Ratings works 
like this: gather rated ballots, then the winner is the candidate with 
the greatest median score.

Even if it's not a very good method, a way to make it summable would be 
of interest to me because it would let me calculate median 
proportionality/BR scores without having to store an array of all n 
scores (for n rounds).

That is, unless the summable version only determines which candidate has 
the greatest median rating (or the order thereof) rather than the actual 
median ratings for the different candidates.