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
Minor wording changes to the problem statements to the first two activities.
Wording changes to the third activities
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 #18 from guangmingyao/yao_dev

Yao dev
Merge pull request #19 from guangmingyao/yao_dev

Yao dev
Added two questions about integration by parts in the laplace transform section.
made changes on week 1 note1--note3
Merge pull request #20 from guangmingyao/yao_dev

made changes on week 1 note1--note3
Added more info on topics in the class and added one more example for the first day.
Merge pull request #42 from KellyBlack/black_dev

Black dev
Added a simple circuit diagram for a resistor.
Minor word changes and the addition of a circuit diagram.
Merge pull request #43 from KellyBlack/black_dev

Minor wording changes for the first lecture and a new image.
marked some texts in color, changed the date
change a typo on page 6