Port build system to setuptools

[sbird]

This fixes Issue #29 and allows a build with python >= 3.12

[jchelly]

I've tried to use this branch to install nbodykit on python 3.12. It mostly works but I think installing the classylss module fails to copy the class data files over to the install location so computing the linear power spectrum in nbodykit (for example) fails because it can't find the data files.

I got it to work by copying these lines from master back into BuildCLib.run in setup.py:

        # copy data files from temp to classlssy package directory
        shutil.rmtree(os.path.join(self.build_lib, 'classylss', 'data'), ignore_errors=True)
        shutil.copytree(os.path.join(self.build_temp, 'data'), os.path.join(self.build_lib, 'classylss', 'data'))

But I have no idea if that's a reasonable fix.

[sbird]

Seems pretty reasonable to me! Thanks.