Use pycodestyle instead of PEP8

PEP8 was renamed to pycodestyle; this issue explains why:
https://github.com/PyCQA/pycodestyle/issues/466

This commit changes our tests to use pycodestyle instead of pep8.

It also means:
- making a couple of whitespace changes to appease the linter
- disabling warnings for bare `Except`s (ie `Except` instead of `Except
  ValueError`) – this seems like a sensible thing to catch but I’m not
  going to make meaningful code changes in this commit

setup.cfg

@@ -1,4 +1,4 @@
-[pep8]
+[pycodestyle]
 max-line-length = 120
-ignore = E402
+ignore = E402, E722
 exclude = ./migrations,./venv,./venv3,./build,./cache