The inclusion of PyOS_ReadlineFunctionPointer in python3dll.c was a mistake.

According to PEP 384:
> functions expecting FILE* are not part of the ABI, to avoid depending
> on a specific version of the Microsoft C runtime DLL on Windows.

https://bugs.python.org/issue43868

Rename Include/symtable.h to to Include/internal/pycore_symtable.h,
don't export symbols anymore (replace PyAPI_FUNC and PyAPI_DATA with
extern) and rename functions:

* PyST_GetScope() to _PyST_GetScope()
* PySymtable_BuildObject() to _PySymtable_Build()
* PySymtable_Free() to _PySymtable_Free()

Remove PySymtable_Build(), Py_SymtableString() and
Py_SymtableStringObject() functions.

The Py_SymtableString() function was part the stable ABI by mistake
but it could not be used, since the symtable.h header file was
excluded from the limited C API.

The Python symtable module remains available and is unchanged.

Py_CompileString() is now always declared as a function by
Include/pythonrun.h. It is overriden with a macro in
Include/cpython/pythonrun.h.

Rename PyPegen* functions to PyParser*, so that we can remove the
old set of PyParser* functions that were using the old parser.

Many PyRun_XXX() functions like PyRun_String() were no longer
exported in libpython38.dll by mistake. Export them again to fix the
ABI compatibiliy.

* Makes symtable.symtable have parity for accepted datatypes
for source code as compile()

* Add NEWS blurb

PEP 432 specifies a number of large changes to interpreter startup code, including exposing a cleaner C-API. The major changes depend on a number of smaller changes. This patch includes all those smaller changes.

available only when Py_LIMITED_API is set to the PY_VERSION_HEX value of
the minimum Python version supporting this API.