Performance optimizations

[breznak]

@chhenning do you have some say for Eigen (vs Blaze) as pybind11 has support for Eigen?

Proposal to introduce pybind for move toward Python 3 compatibility

To answer my own question. As it turns out boost::python has lost some steam and there haven’t been many commits in the recent years. Luckily, a new project pybind11 has arisen for the last few years and I think it looks like a good fit for nupic.core. A few highlights: header only library supports modern c++11 and beyond active development supports python integration of c++ code and embedding python in c++ code has python’s numpy support support for c++'s chrono and Eigen libraries I have…

Also, I’m going to do some refactoring in encoders,SP,TM (maybe touch regions) regarding introducing a common typedef for “SDRvector”, I should probably coordinate this work with your removal of some classes (after you have the PR).