Ranges Iterators: replaced switch-like logic based on Update, with Automatic dispact logic. Added TMIN_SPAN and TMAX_SPAN

Added TIC and AIC function. TIC takes a FitRes, while AIC needs also the number of data point used in the fit

Moved fit_scan from ift_desk to FitRoutines and adapted. Created iterator for looping through the scanned ranges without allocating a dedicated vector

* src/fit_scan.jl: C