Merging my assumptions proof of concept

[Aaron Meurer]

I'd like to merge in my branch with the proof of concepts for the new assumptions (https://github.com/sympy/sympy/pull/2508). It's been sitting for a while now, without much work (mostly due to time limitations on my part). While there is still a lot of work to do, I think it is no longer just a "proof of concept". 

I've renamed newask() to satask(), and put it as a fallback in ask() (i.e., it is called if the existing algorithms to not find an answer). This slows down the new assumptions code a bit, though I think that is acceptable because the new assumptions are not used in very many places. I think the benefits of having this code in master and in use will outweigh these setbacks. Furthermore, I don't have the resources right now to try to make it faster, so my hope is that having it in master will give other people an incentive to look at this as well.

If anyone has any concerns or comments about this, please bring them up on that pull request.  If anyone wants to discuss some of the more technical details of this, such as ideas to speed things up, feel free to bring those up as well.

Aaron Meurer