For Py3.5+, where inittab should really be used instead. For GCC, Clang, MSVC and C++14

Add a dedicated subtype check function for testing against two possible base classes in Py3 (currently used for generator exception checks).

Simplify and clean up the embedded main import code to make it work how it's officially supposed to work: use the inittab.

Avoid generating an "abort()" check for known non-0 steps in prange(). Instead, make it a compile time error if we know it's zero.

Fix optimisation of aligned '%' formats ('%05s', '%-5s') into the correct f-string alignment format.
Closes https://github.com/cython/cython/issues/3476

Floats do not support '{x:d}' formatting and need conversion to 'int' first.
Closes https://github.com/cython/cython/issues/3092

Floats do not support '{x:d}' formatting and need conversion to 'int' first.
Closes https://github.com/cython/cython/issues/3092

Reimplement __Pyx_PyDict_GetItemStrWithError() as a hacky version in Py2 to get the semantics right of returning a borrowed reference with non-KeyError exceptions left in place.

Closes https://github.com/cython/cython/issues/3578

Add comment to explain why "better" GIL handling is not needed in special methods (because it's held anyway).

Closes https://github.com/cython/cython/issues/3590

Test modf, since it's in C89 and has a non-trivial signature.

cimport some C99 float and long double functions, and test legacy kwargs
for double functions.

Adds many long double variants (e.g. expl) that were previously omitted.
No functions have been removed.

I've omitted the identifier for trivial parameters in new functions.
However, I've retained them for existing functions for compatibility
with legacy kwargs.

Classes of functions/macros that are still missing:
 - error-handling ones, like math_errhandling and MATH_ERRNO
 - Bessel functions like j0, y0

Fixes cython/cython#3570

Sorting alphabetically by function name makes it easier to audit
changes.

Also changes "type *" -> "type*"

Closes #3579.

Restore the previous PyThreadState_Get() calls in the refnanny, but with a comment explaining the purpose of the "useless" calls.

Turn all legacy struct fields in the NumPy ndarray type into properties and document them (copied from NumPy docs).
Adapt the 'nogil' declarations according to the ones in NumPy and add some missing functions.
See https://github.com/numpy/numpy/pull/16170

* Support for versioned pxd files like "lib.cython-30.pxd" for a Cython 3.0+ version.
See https://github.com/cython/cython/issues/3573

* Fix test in Py2 by avoiding namespace packages in favour of a normal package.

Remove "PYTHONHOME" setting from embed-test since it seems to break the I/O encoding setup in (at least) Py3.8+ venvs.

See https://github.com/numpy/numpy/pull/16170

Add more 'nogil' declarations to NumPy functions that do not require the GIL (according to the declarations shipped by NumPy itself).
See https://github.com/numpy/numpy/pull/16170

Remove the outdated getbuffer/releasebuffer implementations for the NumPy 'ndarray' since there are probably no NumPy installations out there anymore that do not support the buffer protocol themselves and are still worth supporting.

See https://github.com/numpy/numpy/pull/12284#discussion_r420378155
See GH-3573