Simplex stack variable analysis

Currently, our stack analysis is very naive. To improve the decompilation results, we need more advanced analysis. A good recipe is in one of [Hex-Rays blog posts](http://www.hexblog.com/?p=42).

Implement something like this in RetDec and use it in other analyses as well - e.g. param/return.

@JurajHolub may implement a variant of this for the new x87 FPU stack analysis. So coordinate the efforts and possibly implement only one general analysis that could be specialized for different scenarios.