Remove many lint warnings

Mostly whitespace changes, with max-line-length set to 120
and double-quotes used, adopting black settings.

Related to https://github.com/capnproto/pycapnp/issues/128

.github/workflows/packagingtest.yml

@@ -32,8 +32,8 @@ jobs:
     - name: Lint with flake8
       run: |
         pip install flake8
-        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics --exclude benchmark
-        flake8 . --count --max-complexity=10 --max-line-length=127 --statistics --exclude benchmark
+        flake8 . --filename '*.py,*.pyx,*.pxd' --count --max-complexity=10 --max-line-length=120 --ignore=E211,E225,E226,E227,E231,E251,E261,E262,E265,E402,E722,E999 --show-source --statistics --exclude benchmark,build,capnp/templates/module.pyx
+        flake8 . --count --max-complexity=10 --max-line-length=120 --show-source --statistics --exclude benchmark,build
     - name: Packaging
       run: |
         python setup.py bdist_wheel