Make Python 2.7 division behave like Python 3

[eumiro]

Add from __future__ import division to make Python 2.7 code behave just like Python 3 in an integer division and fix those divisions.

This allows to remove Python 2 numeric hacks that convert an integer to a float to get a float in a division. a/b for two integers now always returns a float.

Do you have any plans to drop support for Python 2.7 anyway?

[karimbahgat]

Thanks! But I think I'll wait with this type of change until we're ready to completely drop Python 2, since that will likely be a larger effort with possible bugs. See my answer to #225.