add of the doc, preperation of the grad and div to get the *arg
changed some mistakes in the grad weights
Modified norm tv according to the new grads
Merge branch 'grad' of github.com:epfl-lts2/pyunlocbox into grad
New version of grad, div with wights (in branch poids).  norm_tv one the way
fix typo and pep8
Merge branch 'poids' into grad

Conflicts:
	pyunlocbox/functions.py