The implementation outsources common operations of AsRVec and AsRTensor
to the PyzCppHelpers.

* Add array interface
* Add tests

use nullptr, reduce includes, remove unnecessary initializer

Use references instead of pointers, use override declarations

Initially ROOT_BINARY_DIR is automatically generated by CMake and equal
CMAKE_BINARY_DIR. Next change is adjusting ROOT_BINARY_DIR used
in ROOTConfig.cmake for ROOT binaries as a ROOTBIN_DIR

Adding a deprecation for uncorrectly used ROOT_BINARY_DIR

This makes ROOT's CMake macros like ROOT_GENERATE_DICTIONARY()
readily available after a successful call to find_package(ROOT),
without having to call include(${ROOT_USE_FILE}), which will
append ROOT's compilation flags to flags of the including project,
potentially overriding them (i.e. -O3 with -O2, etc).

Incorporate the changes of this patch:

https://bitbucket.org/wlav/cppyy-backend/src/master/cling/patches/templ_ctor.diff

spell check

Typos

Fix typos

silenced after commit 466e5825

silenced after commit 466e5825

to the AddEntry function was changed according to the fact that the

None -> null pointer conversion is no longer implemented in Cppyy

If the constructor of the contained object is not run (e.g. because
assembling its arguments triggered an exception), the dtor must not
be run when destructing the cling::Value. Detect this case by imprinting
canary bytes into the contained object bytes: if they have changed,
run the dtor, if not assume that the constructor has failed.

This will cause false positives in those cases where the constructor
is not modifying the first object bytes: in these cases, the dtor
is not run even though the ctor is run. That is still better than
the other case (where the dtor crashes because no ctor was run).

Fix issue with popup (and context) menus popping up on wrong display on Windows with multiple display configuration

Now added for symmetry with surrounding code.