Accelerated coordinate descent for elastic net

This contribution implements the accelerated coordinate descent method for the elastic net based on the paper 
Fercoq, O., & Richtárik, P. (2013). Accelerated, parallel and proximal coordinate descent. arXiv preprint arXiv:1312.5799.
It does not replace the existing coordinate descent code although I also propose some marginal improvements.


you're duplicating a lot of code by creating these new accelerated functions. Can't you use the same functions and just add a "accelerated" parameter ?