Send reminder by mail before the booking start time.

It will be good to have the option to send reminders of the booking by mail on a time basis configured in public bookings.
Adding a checkbox to enable and disable this feature and a text box to set the time along with a select control to define if the time is in days, hours, minutes, etc etc. Then with hook_cron it could send out the reminders. May need to alert about the cron and the time interval for the reminders and also add a reminder mail configuration with the other mail settings.