DOC: typos removed (and pep8)
DOC: typos removed (and pep8)

villalonreina/dipy,FrancoisRheaultUS/dipy,matthieudumont/dipy,FrancoisRheaultUS/dipy,StongeEtienne/dipy,StongeEtienne/dipy,villalonreina/dipy,matthieudumont/dipy,nilgoyyou/dipy,nilgoyyou/dipy