BF: add top-level benchmarking command
BF: add top-level benchmarking command

This allows ``import dipy; dipy.bench()``

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