Perplexity Score for each sentence in each  Seg

Seg ID is contained in file name. The order of sentences is the same as
the order of sentences in Data File

Difference between PPL and PPL1:
Using two different normalizations
counting all input tokens (``ppl'') and excluding end-of-sentence tags
(``ppl1'')

Data Format:
sentence_length    sentence_log_probability   sentence_PPL
sentence_PPL1   avg_PPL_per_word    avg_PPL1_per_word