switch to pyproject.toml

.flake8

@@ -0,0 +1,26 @@
+[flake8]
+# B = bugbear
+# E = pycodestyle errors
+# F = flake8 pyflakes
+# W = pycodestyle warnings
+# B9 = bugbear opinions
+# ISC = implicit str concat
+select = B, E, F, W, B9, ISC
+ignore =
+    # slice notation whitespace, invalid
+    E203
+    # import at top, too many circular import fixes
+    E402
+    # line length, handled by bugbear B950
+    E501
+    # bare except, handled by bugbear B001
+    E722
+    # bin op line break, invalid
+    W503
+    # requires Python 3.10
+    B905
+# up to 88 allowed by bugbear B950
+max-line-length = 80
+per-file-ignores =
+    # __init__ exports names
+    src/flask/__init__.py: F401