* [skip-ci] Fix broken link

* Add missing image

* Add missing image

Co-authored-by: Javier Lopez-Gomez <javier.lopez.gomez@cern.ch>

Fixes https://github.com/root-project/root/issues/8781

There was a problem that the documentation of member functions was
ignored by `print_roofit_pyz_doctrings.py` if there was no PyROOT
documentation for the whole class.

* [skip-ci] Fix formatting issues and add a missing picture

* Better placement of "Figure x"

* Fix wrong link in TSpectrum

* Make sure the pythonisation doc shows up at the end of the classes documentation

* Too many lines were commented out `makeinput.sh`

* Do changes only related to the python Frame placement

* Create the .pyzdoc at the right place.

* Update documentation/doxygen/extract_docstrings.py

add `_out`

Co-authored-by: Enric Tejedor <enric.tejedor.saavedra@cern.ch>

* Add comment

Co-authored-by: Enric Tejedor <enric.tejedor.saavedra@cern.ch>

* a Python decorator is introduced to set the `_cpp_signature` attribute
  of pythonization functions

* the `print_roofit_pyz_doctrings.py` script now also deals with the
  case where `_cpp_signature` is a list of signatures, adding the
  PyROOT block to the documentaton of each function matched by the
  signatures

* the Python docstring is now used to fill the doxygen documentation
  instead of the `_doxygen` attribute

For the documentation of the RooFit pythonizations, we wanted to realize
two things:

  * A PyROOT block in the doxygen documentation of the C++ class,
    indicating the pythonizations for a given class or function

  * A new doxygen page with only the content of all the RooFit PyROOT
    blocks to have a one-stop place to learn everything about RooFit
    pythonizations

This commit proposes a new mechanism to do this, based on the existing
RooFit pythonization mirror class infrastructure:

  * Every class or member function that should get a PyROOT block gets
    an can be patched with an attribute `_doxygen`, containing the
    contents of the PyROOT block
  * Member functions can also be patched with the attribute
    `cpp_signature`, specifying the C++ overload where the PyROOT block
    should go
  * A new scipt `print_roofit_pyz_doctrings.py` extracts this
    information, and this script is used to create a file
    `_roofit.pyzdoc` with all the doxygen source to generate both the
    PyROOT blocks in the existing documentation, as well as the separate
    page about all the RooFit pythonizations

As suggested here: https://root-forum.cern.ch/t/root-reference-guide-broken/45741

Before we used the online version.

These facilities are superseded by valgrind and other memory checkers.
memstat has been deprecated since v6.18.

Keep objstat.

Doxygen was omitting classes that are defined in a .cxx. Although the
interface might not be relevant for users, enabling those should help
developers.

Exclude need to load ROOT files from http server,
allows to use generated documentation directly from local filesystem

No need for extra reading of JSON files from doxygen HTML

* Implement json output for v7 tutorials in the reference guide.

* keep SaveAs