Empty date in options resulted in a error

because of milliseconds in the Date to string conversion.
Merge pull request #18 from basdp/patch-1

Empty date in options resulted in a error
screenshots of ios7 (beta) removed
support of <ios6 only
#15: issue using parameters allowOldDates or allowFutureDates fixed
v.0.2.5
Merge origin/master into ios7