- Do not use globbing
- Use new formatting style
- Propagate compile options and include directories

GetSize is deprecated from 3.3
(https://docs.python.org/3/c-api/unicode.html#c.PyUnicode_GetSize) and
the new recommendation is to use PyUnicode_GetLength.

ROOT-9620 #close

this is done until the present ABI issues between gcc and clang are
solved, most notably the ones concerning shared_ptrs.

[Experimental PyROOT] Rename sources to follow convention of one file per class, introduce helpers for python-side pythonizations

 * PyROOT_PyUnicode_AsString changed return type from char* to const char*
 * Using _PyObject_GC_TRACK results in linking error:
   undefined reference to `_PyGC_generation0'
   The python documentation says this about _PyObject_GC_TRACK:
   "A macro version of PyObject_GC_Track(). It should not be used for
   extension modules."
   So it should not be used. Calling PyObject_GC_Track instead avoids the
   undefined symbol. I also removed the #ifndef R__WIN32 since the
   comment indicates that this was added to avoid the same issue on
   windows. Calling PyObject_GC_Track instead of using the
   _PyObject_GC_TRACK macro should fix the undefined symbol probelem on
   windows too.

This fixes the issue reported on the forum at: https://root-forum.cern.ch/t/windows-10-source-installation-failing-due-to-python-3-bindings/29771

This is an alternative implementation of #2194. Changed Pythonize to
call Evaluate instead of doing Calc on code containing
cling::printValue.

As suggested by Stefan Wunsch, decorators provide a nicer syntax
to mark that a function implements some pythonization.