Update rtastar.hpp

Heuristic store in primary search loop was incorrect.  Was storing f(s') as h(s'); now storing f(s'') as h(s).
Removed line in bestkids which prevented backtracking (caused algorithm to be incomplete).
Removed table update in heuristic function (not mentioned in the original RTA* text).
Merge pull request #36 from dylanoceallaigh/patch-1

Update rtastar.hpp