Additions before turn in

Finish report hw2_jeremy_johnston.odt, updated README.md and added
display of unseen item count to testLM.py.

After testing with high unseen vocab counts, I saw mostly expected
results of ppl values around 300 and even 1000 for really high unseen
counts.

I should likely make generateLM.py reserve prob mass for unseen items,
as for low unseen counts ppl is artificially low (<50), lower than even
ppl for 0 unseen vocab.