TimeToDie Refactoring

TimeToDie Changed - events are ignored, instead hp values are polled,
currently there are three different algorithms on calculating TimeToDie:
 * InitialMidpoints
 * LeastSquared
 * WeightedLeastSquares (default)

It can be changed by setting
'jps.timeToDieFunction = "WeightedLeastSquares"'.

All algorithms based on TimeToDie Addon: http://www.curse.com/addons/wow/timetodie

It polls target, focus, mouseover and boss* - if you're a healer also party*, partypet*, raid* raidpet*, arena*, arenapet*