Extracted and exposed scrollToDate:animated method
Calculate date range from given date
[Update] Rename some variables in the method `scrollToDate:animated:`.
[Fix] An initial mark image.
[Update] Improve the data source of `RSDFDatePickerView`.

Replace the method `datePickerViewMarkedDates:` by two new methods
`datePickerView:shouldMarkDate:` and
`datePickerView:isCompletedAllTasksOnDate:`.
Resolve #21
[Update] README.

DataSource (optional).
Version bump (0.5.0)
Not default FirstWeekDay fix;
Relocate util method;
Better solution for #16