Allow specific date to be set instead of a "weekday" #82

Is your feature request related to a problem? Please describe.
I'd like to put specific dates for meetings in the CSV file, instead of having to put in a weekday, so that I can use zoomrec to record one-off Zoom meetings.

Describe the solution you'd like
The addition of a date column, and perhaps a weekly/regular boolean column to allow the toggle of regularly joining the same meeting or not.

This is the same request as #55