change numpy arrays to memmaps to reduce memory usage
change numpy arrays to memmaps to reduce memory usage

samuelstjean/dipy,sinkpoint/dipy,villalonreina/dipy,beni55/dipy,matthieudumont/dipy,demianw/dipy,samuelstjean/dipy,nilgoyyou/dipy,villalonreina/dipy,sinkpoint/dipy,Messaoud-Boudjada/dipy,beni55/dipy,JohnGriffiths/dipy,jyeatman/dipy,Messaoud-Boudjada/dipy,FrancoisRheaultUS/dipy,matthieudumont/dipy,jyeatman/dipy,mdesco/dipy,FrancoisRheaultUS/dipy,demianw/dipy,rfdougherty/dipy,oesteban/dipy,StongeEtienne/dipy,nilgoyyou/dipy,rfdougherty/dipy,samuelstjean/dipy,oesteban/dipy,JohnGriffiths/dipy,mdesco/dipy,StongeEtienne/dipy