See https://github.com/cython/cython/issues/3573

Tighten "numpy_attributes" test to assert that it's actually using a property call and not an attribute access.
Also add a test for the newly added "ndarray.data" property.

Mark the embedded C main() function in the embedding test as "extern C" in C++ to see if that fixes the C++ builds in MSVC.

Fix a C compiler warning about unused cleanup code in buffer using functions that always raise (found by clang in the bufaccess.pyx test).

* Rewrite C property support (GH-2640) based on inline C methods.
Supersedes GH-2640 and GH-3095.
Closes GH-3521.

* Test fix for `numpy_parallel.pyx`: avoid depending on whether "nd.shape" requires the GIL or not.

* Turn NumPy's "ndarray.data" into a property to avoid direct struct access.

* Make "ndarray.size" accessible without the GIL.

Prevent VerboseCodeWriter from inserting nul-bytes into the C file by switching to a more "standard" way of inserting code at a later time.

Improve error handling in "cython.array" creation code to avoid calling Py_BuildValue() with an exception set if "__pyx_format_from_typeinfo()" failed.

Avoid unnecessary int-object creation when formatting numbers as strings in format_from_typeinfo() utility function.

Improve error handling in "cython.array" creation code to avoid calling Py_BuildValue() with an exception set if "__pyx_format_from_typeinfo()" failed.

Refactor step handling in slice_memviewslice() utility code to make it more obvious what is happening in which case.
Closes GH-3568.

Avoid useless resorting to char* in nogil code in MemoryView.pyx for raising exceptions, since constant Python strings are just fine there.