Merge branch 'master' of https://root.cern.ch/git/root

docbook/users-guide/ALittleC++.md

docbook/users-guide/AddingaClass.md

docbook/users-guide/CINT.md

docbook/users-guide/CollectionClasses.md

docbook/users-guide/ExampleAnalysis.md

docbook/users-guide/FittingHistograms.md

docbook/users-guide/FoldersTasks.md

docbook/users-guide/Geometry.md

docbook/users-guide/GettingStarted.md

docbook/users-guide/Graphics.md

docbook/users-guide/Graphs.md

docbook/users-guide/Histograms.md

docbook/users-guide/InputOutput.md

docbook/users-guide/InstallandBuild.md

docbook/users-guide/Introduction.md

docbook/users-guide/LinearAlgebra.md

docbook/users-guide/MathLibraries.md

docbook/users-guide/ObjectOwnership.md

docbook/users-guide/PhysicsVectors.md

docbook/users-guide/PythonRuby.md