story status loosely follows tasks

platform:  # supported: 2.0.4, 2.1.5, 2.2.0
backlogs:  # supported: 0.9.32
ruby:  # supported: 1.9.3, 1.8.7

updates / replaces #292

This is the implementation of
 a) the original simple closing of stories
 b) the loose following by averaging done_ratios for both redmine setting issue-done-ratio by status and by field

The behavior is not really self-explanatory, but i believe starting from here the inclined requirements engineer can start refining ;-)

Hope that helps.