Adds new freeze and enables manipulating timeIntervalSinceReferenceDate

Added parameterless freeze method to TUDelorean.
Added delorean_timeIntervalSinceReferenceDate so that it uses the time
jump when calling [NSDate timeIntervalSinceReferenceDate].
Removed Appendix from License file
Merge pull request #1 from vcorugedo/master

Extend functionality by freezing [NSDate timeIntervalSinceReferenceDate] when necessary