`datetime.timestamp` returns `float`, but Arrow's returns `int`

As mentioned in https://github.com/crsmithdev/arrow/pull/464 (thanks @zmwangx!), Python 3.3 added a datetime.timestamp() method returning a float with microsecond precision. Unfortunately, Arrow already has an Arrow.timestamp property, which is an int with second precision.

As Arrow is intended to be a drop-in replacement for datetime, my opinion is that this forces us to implement a timestamp method as well. We can implement this and maintain backwards compatibility if the timestamp property returned an int-like object that, when called, returned a float. Accessing it like a property could be accompanied with a DeprecationWarning so we could remove this hack eventually.

[jadchaar]

Hi @Syeberman, I am looking to fix this issue and was wondering where to start. I was looking at arrow.py and noticed that there is a float_timestamp method, and was wondering if this is as simple as creating a method called timestamp() and simply mimicking the functionality of float_timestamp (reducing duplicate code of course). Any input is appreciated 😄 .

[systemcatch]

https://github.com/sdispater/pendulum/issues/71 might be a useful reference.