(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
This is statement is void as such. Which type of discourse are you referring to?

(Also, I think the principle is to have a full description of the function in the doctring, without implicating the function name)