See http://fastml.com/gender-discrimination/ for description.
prep_data.py - a first step
chunk_by_authors.py - a utility for preparing a validation set
split_by_authors.py - a utility for preparing a validation set
f_sigmoid.r - sigmoid function
f_log_loss.r - log loss function for scoring
f_normalize_to_01.r - a utility function for using with linearRidge()