Migrate functions from NumericExtensions

[Dahua]

With the latest upgrade of the NumericExtensions package, the performance of some reduction functions are considerably improved. 

The sum, maximum/minimum functions are considerably more efficient than the ones in Base (e.g. sum(x) is 2x faster with the same level of accuracy using cascade sum, and ``sum(x, 1)`` is nearly 3x faster, and sum(x, 2) is nearly 10x faster). 

In the new implementation, these functions no longer rely on functors, which make them easier to migrate. If there's no objection, I will work on a PR to julia base soon.

[John Myles White]

That's great. Well done, Dahua!

-- John

[Stefan Karpinski]

That is great. What, if anything, stands in the way of moving some of these implementations into Base?

[Dahua]

In version 0.2.x, this implementation relies on functors, which I don't feel like moving to the base.

Now, for several key functions, the implementation no longer relies on functors. And, I will work on moving them to Base soon.

- Dahua

[Stefan Karpinski]

Ah, right. That makes a lot of sense. Hopefully the need for functors will go away in the near future.