Switch Date Handling Routines to use DateTime internally

[MarkBaker]

Switch Date Handling Routines to use DateTime internally (to avoid use of unix Timestamp and ensure full range of Excel DateTimes on 32-bit systems), and use DateTimeInterface for typehinting so that DateTime or DateTime immutable can both be used

[PowerKiKi]

Is anybody working on that ? I would be willing to do it if the work has not already started and also fix date related unit tests at the same time. What do you say ?

[MarkBaker]

I've been working on the DateTime class, switching it to work with DateTime objects rather than unix timestamps, and using DateTimeInterface where appropriate

[PowerKiKi]

ok, then I won't do anything about that. I'll have a look at fixing other unit tests.

In the meantime could you please enable Travis CI for this repository ? The badges are shown in the README, but Travis has nod builds to show...

[PowerKiKi]

Is it correct that this is now finished ?

[PowerKiKi]

Assuming this done