When checking whether an appointment belongs to a given day in
apoint_inday(), the return value was 0 if the end time of the
appointment matched 00:00 on that day (because we do not want to include
appointments starting on the day before and lasting until midnight).
However, this means that punctual appointments at 00:00 were not
included in any day. Fix the apoint_inday() logic to take this into
consideration.
Fixes GitHub issue #39.
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>