Fixed timezone issue when using parse_date
guess_address() fails gracefully when there is no internet connection
add_presentation() documentation.presenter_address, when setting presenter
information in semnar objects, using a semnar_presenter object.event() creates a semnar_event object with event details, which
can be passed in add_presentation()'s event argument.get_event() and set_event() for getting and setting event
information in semnar objects.start is before end in
add_presentation(), when both are specified.add_presentation() returns an error if start date/time is after end date/time.add_presentation() now supports type = "webinar".%>% pipe to base pipe |>.<<-guess_address method for reverse geolocation of presentations using the OpenStreetMap API