Update flake8 config

Author: jwodder

setup.cfg

@@ -1,12 +1,11 @@
 [flake8]
 doctests = True
-exclude = .*/,build/,dist/,test/data,venv/
-hang-closing = False
+extend-exclude = build/,dist/,test/data,venv/
 max-doc-length = 100
 max-line-length = 100
 unused-arguments-ignore-stub-functions = True
-select = C,B,B902,B950,E,E242,F,U100,W
-ignore = B005,E203,E262,E266,E501,W503
+extend-select = B901,B902,B950
+ignore = A003,B005,E203,E262,E266,E501,U101,W503
 
 [isort]
 atomic = True