Created new branch for week1 development.
Revised for Python tutorial
Added files for week3 branch
added folders
Expectation-Maximization code added. Typo fixed.
Merge branch 'week1_bob' of github.com:brittlundgren/py-astro-stat
Merge branch 'week2_britt' of github.com:brittlundgren/py-astro-stat
Merge branch 'week3' of github.com:brittlundgren/py-astro-stat
Merge branch 'week4' of github.com:brittlundgren/py-astro-stat
Reorganized master branch