Corrects a bug on closest/farthest and extends functionality to take *tuple

[ghost]

The closest/farthest functions didn't actually consider the distance between the current instance and the two parameters. On master, the 'smaller'/'bigger' was returned regardless of the actual distance between the instance and the parameters.

>>> a = pendulum.now()
>>> b = pendulum.now() + pendulum.duration(hours=10)
>>> c = pendulum.now() + pendulum.duration(hours=-15)
>>> a.closest(b,c) == c
True
>>> # however, the closest is actually b
>>> # similarly, using farthest, should return C but instead returns b :
>>> a.farthest(b,c) == b
True

In addition, I have extended the functionality to receive unpacked iterables, through * operator while keeping the initial signature and backwards compatibility.

For some reason this Travis build failed but mine worked.

https://travis-ci.org/oddProton/pendulum/builds/406625985

[ghost]

Can you check it out and tell me what you’d like for the pull to go through?

[sdispater]

Thanks!