Enhanced word weighting mechanism

The new relevance weight of a word is, sum over max(0, 1 - log(level_occurance))
Signficance level is, as usual, min(level_occurance)
Frequency weight of a term is, tf(k + sig_level) / sig_level(k + 1)
Normalization is done to both relevance and frequency weights
Final word weight from a passage is, (1 - alpha) * n_rWeight + alpha * n_fWeight

All these configuration are specified in WeighingConfiguration.java