api: use time.Time instead of int64

[dolmen]

Suggestion for API change: use time.Time instead of int64 in the exposed API. That would be more idiomatic.

[dolmen]

@nightwolfz You voted against this proposal. Could you explain?

[yusufozturk]

I think in general using Epoch value is much safer. Quartz returns an interval value which is a total number of nanoseconds/milliseconds/seconds etc. So taking Epoch value as an input and adding quartz interval on top of it is much easier and safer option for the library.

With Epoch value, you can easily escape from timezone problems and It's very easy to convert time into the Unix time.

[yusufozturk]

A similar issue when timezone is in place:
#33