[TDF][VecOps] Add tutorial with a real analysis usecase

[dpiparo]

which shows how the programming model can be slimmed down using
TDF and VecOps comparing with the classical PyROOT approach, TTreeReader
and TDF without VecOps.

[phsft-bot]

Starting build on centos7/gcc49, mac1013/native, slc6/gcc49, slc6/gcc62, slc6/gcc62, ubuntu16/native, ubuntu16/native, windows10/vc15 with flags -Dvc=OFF -Dimt=ON -Dccache=ON
How to customize builds

[phsft-bot]

Build failed on slc6/gcc62.
See console output.

Failing tests:

• projectroot.roottest.python.JupyROOT.roottest_python_JupyROOT_importROOT

[phsft-bot]

Starting build on centos7/gcc49, mac1013/native, slc6/gcc49, slc6/gcc62, slc6/gcc62, ubuntu16/native, ubuntu16/native, windows10/vc15 with flags -Dvc=OFF -Dimt=ON -Dccache=ON
How to customize builds

[phsft-bot]

Build failed on slc6/gcc62.
See console output.

[phsft-bot]

Build failed on slc6/gcc49.
See console output.

Errors:

• ERROR: Timeout after 10 minutes
• ERROR: Error fetching remote repo 'origin'
• stderr: error: RPC failed; result=18, HTTP code = 200
• ERROR: Error fetching remote repo 'origin'

[phsft-bot]

Build failed on ubuntu16/native.
See console output.

Warnings:

• /mnt/build/workspace/root-pullrequests-build/root/graf2d/qt/src/TGQt.cxx:1151:7: warning: assuming signed overflow does not occur when assuming that (X + c) < X is always false [-Wstrict-overflow]
• /mnt/build/workspace/root-pullrequests-build/root/graf2d/qt/src/TGQt.cxx:1126:7: warning: assuming signed overflow does not occur when assuming that (X + c) < X is always false [-Wstrict-overflow]

Failing tests:

• projectroot.roottest.root.multicore.roottest_root_multicore_tp_process_imt