Added flag fit_mode=2 and set to default.
Added a setter for the stub references.
Added x, y, and rho to the hit structure.
Added event and triggerTower IDs with the setter functions.
Added code for the retina fitter.
Fixed bug in eta_range assignment.
Merge pull request #37 from casarsa/RetinaFitter

Pull Retina fitter from Massimo