(WIP) Sparse models: S-LASSO and TV-l1

- Supports TV-l1 and S-LASSO priors
- Supports logistic and squared losses
- Has cross validation
- Can automatically select alpha by CV (+ automatic computation of useful alpha ranges for the CV)
- Warning: User must supply l1_ratio
Well, actually lambda is discouraged. It gives code that is hard to read.

I would strongly prefer if the use of lambda could be minimized.

And nobody care about lisp anymore :P