Added Chat features

-Announces when someone new takes the #1 spot on top 5
-Messages the player on kill/death their rating change
-Added a ranking to chat for top 5 (e.g. "[1st]<Denevien> Hello
Friends!"
-Tweaked how kill decay works. Now keeps 10 most valuable kills in the
past 2 weeks (as opposed to last 10 kills in past 2 weeks).