Convert root file to txt, csv file

[ferhue]

some (loosely related) ideas:

• rootls
• GitHub - ivankp/rootbr: Command-line utility for inspecting contents of CERN ROOT files.
• TBrowser alternative for non-X11 mode
• TGraph SaveAs .csv · Issue #9491 · root-project/root · GitHub
• THistSaveAs txt or csv · Issue #10474 · root-project/root · GitHub