new-style string formatting in root2hdf5 and remove use of io.utils and implement --update mode to append to existing files
new-style string formatting in root2hdf5 and remove use of io.utils and implement --update mode to append to existing files

ndawe/rootpy,rootpy/rootpy,rootpy/rootpy,rootpy/rootpy,kreczko/rootpy,kreczko/rootpy,ndawe/rootpy,ndawe/rootpy,kreczko/rootpy