No longer need to wrap the stabs_log_pointer, as we only ever take 500 samples.
Remove duplicate common language filtering from tree loading function.
Use more IE trees to get a more accurate distance vector.
Better structuring and commenting to make it clearer how the authoritative vectors are constructed, normalised, combined.
Use stored authoritative combo vector, rather than re-concatenating each time.
If we have more of one language family than the other, select a random subset of the larger family so that the two families are equally sized.  This makes our model fitting more fair.
Changed logic of fit_model function: fits only one model and returns correlations for the individual families.
Refactor optimise_geographic and optimise_genetic to follow new form of fit_model.
Big ugly, inelegant bulk commit of many logically independent changes.  The gist is that the two tasks of fitting models to the combined data and assessing the fit against the individual families is now much more clearly separated.
Use pre-defined string for BWO feature.
Use mean values for feature distances with no data, rather than 0.5.