Tutorial ABCD method with RooParamtricHist

[cesarecazzaniga]

Pull request to propose a small tutorial to illustrate the application of RooParametricHist for a per-bin ABCD method in Combine.

Material added in the PR:

documentation for the tutorial
codes to generate input datasets, workspaces and cards to run the tutorial

[cesarecazzaniga]

I went through your comments, and i have modified the tutorial accordingly. First, in the generation of the files i have fixed the seed such that we should all get the same results. Second, i have noticed a small issue in the datacards generation code that was creating the large r fitted value you were noticing, and i fixed it. I have added the results one should get to the tutorial and the new plots. Moreover i have added, as suggested, the commands to really reproduce each step.

[cesarecazzaniga]

added uncommitted changes for create-workspace.py, updated documentation to match naming of files from most recent version of combine, updating results to match the ones from the latest version