Memory-allocator

Update cython version number for compatibility with python 3.11.

This release provides prebuilt wheels.

Fix test failures on 32bit systems.

This is the first release of the `MemoryAllocator` independent of SageMath.

The dependency on `cysignals` has been removed to make it more portable (Windows) and the testing infrastructure has been updated.

Removed `__init__.py` that was accidentally imported along the history of `memory_allocator.pxd` and `memory_allocator.pyx`.

Initial release of **memory_allocator**. The code is factored out of https://github.com/sagemath/.

The dependency on `cysignals` has been removed to allow easy installation on windows. Otherwise the code should function exactly the same. Change `from sage.ext.memory_allocator cimport MemoryAllocator` to `from memory_allocator cimport MemoryAllocator`.