Error on fullday-event: can't compare datetime.datetime to datetime.date

When trying to export a full-day event, I get a crash:

```
$ python3 ical2csv.py --include-full-day=1 fullday.ics
UID,CREATED,LAST-MODIFIED,DTSTART,DTEND,SUMMARY,LOCATION
Traceback (most recent call last):
File "ical2csv.py", line 151, in
args.include_full_day):
File "ical2csv.py", line 52, in process
if (start_date is not None and start_date > item_start) or end_date < item_end:
TypeError: can't compare datetime.datetime to datetime.date
```

----

```
BEGIN:VCALENDAR
PRODID:-//Mozilla.org/NONSGML Mozilla Calendar V1.1//EN
VERSION:2.0
BEGIN:VTIMEZONE
TZID:Europe/Berlin
BEGIN:DAYLIGHT
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:19700329T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=3
END:DAYLIGHT
BEGIN:STANDARD
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:19701025T030000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
END:STANDARD
END:VTIMEZONE

BEGIN:VEVENT
CREATED:20151218T191453Z
LAST-MODIFIED:20151222T082058Z
DTSTAMP:20151222T082058Z
UID:euv2mqhvb4i9mp3an827m185v0@google.com
SUMMARY:test
STATUS:CONFIRMED
DTSTART;VALUE=DATE;TZID=Europe/Berlin:20151223
DTEND;VALUE=DATE;TZID=Europe/Berlin:20160104
TRANSP:TRANSPARENT
SEQUENCE:0
X-DEFAULT-ALARM:TRUE
END:VEVENT

END:VCALENDAR
```