* change g2rating,etc. to attr_reader (instead of attr_accessor)
* move @dvolatility into DVOL constant
* add p_win
* make comparison operator use p_win(self,other)
* use << when adding to results array instead of .push()
* improved comments; mostly from Glicko2 document
* minor variable renaming to improve readability
* clear results array after ratings are finally updated (no functional change, just cleaner)
swaits