Format and lint codes and fix packaging (#125)

* add: configure files (setup.py->setup.py+setup.cfg+pyproject.toml)

* add: __download_url__

* format with black and isort

* fix: flake8 section in setup.cfg

* add: E501 to flake ignore

* fix: metadata.name does not accept attr

* fix: merge __version__.py into __init__.py

* fix: flake8 errors in tests/

* fix: datetime.datetime -> datetime

* fix: banner

* fix: ignore W605 for banner

* fix: way to install deps in CI

* add: versem to setuptools

* fix: drop python<=3.6 (#126) from package and CI

tests/test_utils.py

@@ -1,9 +1,9 @@
+from waybackpy import __version__
 from waybackpy.utils import (
-    latest_version_pypi,
-    latest_version_github,
     DEFAULT_USER_AGENT,
+    latest_version_github,
+    latest_version_pypi,
 )
-from waybackpy.__version__ import __version__
 
 
 def test_default_user_agent():