Instead, test for libC++ and language version.
This fixes MacOS builds with >=C++14 and tests enabled.

The RooFit release notes were slightly outdated after the deprecation
macro R__SUGGEST_ALTERNATIVE had been merged.

This prevents the vector to be reallocated if the size exceeds the capacity of
the vector causing invalid pointer accesses.

Fixes ROOT-7749.

When a RooDataSet is constructed without a weight variable, weights are ignored when events
are added to the dataset. Now, there will be a clear warning notifying the user that an event
weight is being ignored.
The documentation has also been updated.

See also:
https://root-forum.cern.ch/t/fit-to-a-weighted-unbinned-data-set/33495

* Fix doxygen generation with Python 3

* Adjust tutorials for doxygen documentation generation.
When run inside the makeimage.py wrapper during doxygen generation the
variable scope is different than when the tutorials are run stand-alone.
The change in tutorials/math/tStudent.py is Python 3 specific and is due to
that list comprehensions in Python 3 are run in an implicit function scope.

The new release includes some improvements in both Forward and
Reverse mode:
* Extend the way to specify a dependent variables. Consider function,
  `double f(double x, double y, double z) {...}`, `clad::differentiate(f, "z")`
  is equivalent to `clad::differentiate(f, 2)`. `clad::gradient(f, "x, y")`
  differentiates with respect to `x` and `y` but not `z`. The gradient results
  are stored in a `_result` parameter in the same order as `x` and `y` were
  specified. Namely, the result of `x` is stored in `_result[0]` and the result
  of `y` in `_result[1]`. If we invert the arguments specified in the string to
  `clad::gradient(f, "y, x")` the results will be stored inversely.
* Enable recursive differentiation.
* Support single- and multi-dimensional arrays -- works for arrays with constant
  size like `double A[] = {1, 2, 3};`, `double A[3];` or `double A[1][2][3][4];`

See more at: https://github.com/vgvassilev/clad/blob/v0.5/docs/ReleaseNotes.md

- when ROOT::IsEnableImplicitMT() TMVA will run by default in MT
- when TMVA::gConfig().EnableMT(0) or TMVA::gConfig().EnableMT(nthreads > 1)  TMVA will run in MT independently of ROOT::IsEnabledImplicitMT()
- when TMVA::gConfig().EnableMT(1) or TMVA::gConfig().DisableMT()  TMVA will run sequentially and its thread pool will be released 

since it is a special class: we are not interested in the actual
layout, it is opaque for the ROOT IO being it part of the STL.

webui should always be build with root7, if other is not specified

Show correspondent status message

It should be possible build root7, but not build webui

using a static assert. The error prompted by dictionary generation is:
```
input_line_9:7:1: error: static_assert failed "ClassDef(Inline) macro: the specified ID is not an integer."
ClassDef(A, 1.4f)
^~~~~~~~~~~~~~~~~
/Users/danilopiparo/RootDevel/Root6/head/build/include/Rtypes.h:326:4: note: expanded from macro 'ClassDef'
   _ClassDefOutline_(name,id,virtual,)   \
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/danilopiparo/RootDevel/Root6/head/build/include/Rtypes.h:300:4: note: expanded from macro '_ClassDefOutline_'
   _ClassDefBase_(name,id, virtual_keyword, overrd)       \
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/danilopiparo/RootDevel/Root6/head/build/include/Rtypes.h:271:4: note: expanded from macro '_ClassDefBase_'
   static_assert(std::is_integral<decltype(id)>::value, "ClassDef(Inline) macro: the specified ID is not an integer.")...
```

Given a class T, with a constructor with signature T(P0, P1, ..., PN),
it is possible to initialise an RVec<T> with the following syntax:
```
auto RVec<P0> p0 {...};
auto RVec<P0> p1 {...};
// ...
auto RVec<PN> pN {...};
auto vecT = Construct<T>(p0, p1, ..., pN);
```
For example, it allows to build RVecs of LorentzVectors:
```
RVec<float> etas {.3f, 2.2f, 1.32f};
RVec<float> phis {.1f, 3.02f, 2.2f};
RVec<float> pts {15.5f, 34.32f, 12.95f};
RVec<float> masses {105.65f, 105.65f, 105.65f};
auto fourVects = Construct<ROOT::Math::PtEtaPhiMVector>(pts, etas, phis, masses)
```

Upgrade to the newest three.js, updates for geometry viewer
This is preliminary 5.7.0 release

delivered

Such model used only there, other widgets do not need this model.
Allows to use browser in different places more easy

required

String path is more flexible (but more slow) way to address items in the
hierarchical structures. Now communication with browser component will
be redone with strings

For geometry viewer one do not need Component.js, central view can be
used as is

Main point - creation of specialized Model and ListBiniding for brwoser.
It is very unpracticale to use them with Component.js - making code not
modular

When browser obtains full hierarchy description, no extra requests are
required. But also one should not delete existing elements as partial
browser is doing 

Now it always single node, but many elements can be assigned to the
top-level. To simplify handling, "invisible" top-level element is
introduced. It always there and corresponds to "/" address

Let use RBrowserItem as is on the client