140527 Added DayClass

Created DayClass, overwrites get_start, get_end, duration
Created span(), as opposed to duration
Created count()
Added to_days and to_events, to DataStore.  Converts dat to specified scale
Added data type checking, to prevent inappropriate conversions
TODO Create WeekClass
TODO Handle type and conversion between different EventClass subclasses
TODO Create abstracts and error handling for Eventclass.fmt()
TODO Map data for reporting and data analysis