Better TOCs at the beginning of classes headers (#7951)

core/base/src/TAttFill.cxx

core/base/src/TAttLine.cxx

core/base/src/TAttMarker.cxx

core/base/src/TAttText.cxx

core/base/src/TColor.cxx

documentation/doxygen/Doxyfile

graf2d/graf/src/TGaxis.cxx

graf2d/graf/src/TLatex.cxx

graf2d/graf/src/TPaveStats.cxx

hist/hist/src/TF1.cxx

hist/hist/src/THStack.cxx

hist/hist/src/TMultiDimFit.cxx

hist/hist/src/TMultiGraph.cxx

hist/histpainter/src/TGraphPainter.cxx

hist/histpainter/src/THistPainter.cxx

io/doc/TFile/README.md

math/matrix/doc/index.md

math/vecops/inc/ROOT/RVec.hxx

tree/dataframe/src/RDataFrame.cxx

tree/tree/src/TTree.cxx