Fix typo
Merge pull request #113 from dmcdougall/patch-1

Fix typo
change all plt to pyplot

also renamed module 4 lessons to add prepended module number for
consistency across modules.  all notebooks have been run for
presentation
Merge pull request #116 from numerical-mooc/pyplot

change all plt to pyplot
Update broken links
Merge pull request #1 from numerical-mooc/master

please update my fork