Merge pull request #40 from KellyBlack/black_dev

Merge additional activities and a reordering of the activities based on the new schedule.
Merge branch 'master' into yao_dev
Merge branch 'black_dev' of https://github.com/KellyBlack/ODE-Recitation-Activities into yao_dev
Merge pull request #41 from KellyBlack/black_dev

Made minor changes to the wording of some activities.
missing information in activity 15 is added
Merge branch 'yao_dev' of github.com:guangmingyao/ODE-Recitation-Activities into yao_dev
Merge pull request #19 from guangmingyao/yao_dev

Yao dev