Python 3 Compatibility for Vec3

[Swiftloke]

This commit adds the __eq__ and __ne__ functions to the Vec3 class, enabling equal and not equal comparisons of the class in Python 3. Discussion should be had on support for __gt__, __lt__, __ge__, and __le__.

[arpruss]

Why not just define eq as return self.x == rhs.x and self.y == rhs.y and self.z == rhs.z ?

[Swiftloke]

There really is no reason why not, I suppose. I just copy/pasted the __cmp__ code from the Py2 implementation and made it work for Py3- I wasn't really sure if you would want the code to look similar.