New implementation of the linear part. No more slope but slope differences. This gives the true nlog(n). Practically this has shown to reduce the computational time by more than half.

correction of quadratic swap, Etoile. Addition of a print method.

Inclusion of vector of quadratic class + serial push methods and optim solver. Works fine on example. Still 10 time slower than the linear counterpart

TODO : bi dimensional
       re-implement quadratic to have the true nlog(n) (i.e. not with slopes but with slopes diffs)