Merge pull request #29 from mattgiguere/master

S17 Merged
updated from hack day later bits
chapter 9 first half

ipnb of first half of chapter 9 of astroML book, covering
classification w Bayes method, k neighbors, and logistic regression
Merge pull request #30 from ih64/master

chapter 9 first half
first commit
Merge pull request #31 from duncandc/master

added decision tree notebook.
Merged with upstream and added Ch 10 notebook.