Rework API to take `time.Time`

[Psykar]

A few methods in the API take year/month/day/hour/minute/second
Would you be against changing this to take a time.Time object instead?

We could either bump up major versions (v2) or just add a new set of methods that live side by side.

Thoughts?

[joshuaferrara]

My initial desire was to port the library as close to the original as possible. I'd think for convenience sake though, converting the API to take time.Time would be appropriate and something that I'd look forward to. I also can't think of any good reason to hold back the library from using what modern constructs are available in Go.