NF - added trilinear interpolation function for tracking
NF - added trilinear interpolation function for tracking

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