ZeroK: Ladder rework

From ZeroK: link to original post

Ladder ratings have been modified to be more intuitive. Now your ladder rating will always increase when you win a game and decrease when a game is lost. The rank brackets are now global and equal for all users. Once you reach a 20% threshold in the next bracket, you will rank up. Once you go more than 20% below your current bracket, you will rank down. Ratings will change less between games.

The way this is implemented is with two major changes. Firstly, ladder rating is only updated playing a game. So there will be no rating changes when you're not playing and it will never go opposite to whether you won/lost. Additionally, the rating changes use a moving average to smooth out changes. Secondly, the target rating for the ladder rating is now a monthly average. This means that instead of just looking at your most recent rating, your rating over the whole past month will be averaged, weighted by the number of games played each day. This should make for more stable monthly ladders.

There's also been a fix for people who haven't played within the last 30 days still being displayed on the ladders. This means that there will be less rated players, and thus less purple ranks (top 1%).