add pyproject.toml, fix sys.path, fixes #6466

setup.py: add parent to sys.path

When using pyproject.toml the parent of setup.py is not on sys.path by default.

See <pypa/setuptools#3134>.

pyproject.toml

@@ -0,0 +1,3 @@
+[build-system]
+requires = ["setuptools", "pkgconfig", "Cython"]
+build-backend = "setuptools.build_meta"

setup.py

@@ -19,6 +19,7 @@
 except ImportError:
     cythonize = None
 
+sys.path += [os.path.dirname(__file__)]
 import setup_checksums
 import setup_compress
 import setup_crypto