setup.py: Declare development and test dependencies properly

There is no 'test_requires' argument to setuptools.setup(). Instead,
pass extras_require with appropriate keys for the other kinds of
dependencies.

Add the development dependencies outlined in README.md.

All dependencies can now be installed with:

  pip install -e .[dev,test]

Author: jherland

setup.py

@@ -18,7 +18,7 @@
         "License :: OSI Approved :: Apache Software License"
         "Operating System :: OS Independent",
     ],
-    install_requires=["pycryptodomex", "scalable-cuckoo-filter"],
-    test_requires=["pytest"],
     python_requires=">=3.6",
+    install_requires=["pycryptodomex", "scalable-cuckoo-filter"],
+    extras_require={"dev": ["black", "flake8", "pre-commit"], "test": ["pytest"]},
 )