New Spatial Pooler example

Hi folks! We have added a new spatial pooler example to nupic. You can find it in the NuPIC repo at examples/sp/

It comes with annotations within the source file. It has the purpose of presenting some basic properties of the spatial pooler, and to reproduce Figs. 5, 7 and 9 from this paper: It should serve as an introduction to the concept of spatial-pooling to newbies. Cheers!