this allows to create files with this factory pattern

myFile = ROOT.TFile.Open("myfile.root")

the pythonizations are three:
1. A C++ pyz to provide attr syntax. For example:

myfile.mydir.mysubdir.myHist.Draw()

2. A C++ pyz to allow users to invoke the templated method TDirectory::WriteObject<T>. For example:

h = ROOT.TH1F("h","",10, 0, 1)
myfile.WriteObject(h)

3. a Python pyz which implements TDirectory::Get in terms of the pythonized attr syntax

Eliminate previous redundancy with namespace.

Includes a new mechanism for adding pythonizations and two examples
of pythonizations for TTree that have been ported on top of the
new Cppyy API (one in Python, one in C++).