Level 8. Dates and Times

[therizhao]

Teach Duke how to understand dates and times. For example, if the command is deadline return book /by 2/12/2019 1800, Duke should understand 2/12/2019 1800 as 2nd of December 2019, 6pm, instead of treating it as just a String.

Minimal: Store deadline dates as a java.time.LocalDate in your task objects. Accept dates in a format such as yyyy-mm-dd format (e.g., 2019-10-15) and print in a different format such as MMM dd yyyy e.g., (Oct 15 2019).
Stretch goal: Use dates and times in more meaningful ways. e.g., add a command to print deadlines/events occurring on a specific date.