Add linting workflow

.flake8

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+[flake8]
+max-line-length=110
+docstring-convention=all
+import-order-style=pycharm
+exclude=constants.py,__pycache__,.cache,.git,.md,.svg,.png,tests,venv,.venv
+
+ignore=
+    B311,W503,E226,S311,T000
+    # Missing Docstrings
+    D100,D104,D105,D107,
+    # Docstring Whitespace
+    D203,D212,D214,D215,
+    # Docstring Quotes
+    D301,D302,
+    # Docstring Content
+    D400,D401,D402,D404,D405,D406,D407,D408,D409,D410,D411,D412,D413,D414,D416,D417
+    # Type Annotations
+    ANN002,ANN003,ANN101,ANN102,ANN204,ANN206
+    # Whitespace Before
+    E203

.github/workflows/linting.yml

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+name: Linting
+
+on: [push, pull_request]
+
+jobs:
+  lint:
+
+    runs-on: ubuntu-latest
+
+    env:
+      PIP_CACHE_DIR: /tmp/pip-cache-dir
+
+    steps:
+      - name: Checks out repository
+        uses: actions/checkout@v2
+
+      - name: Set up Python 3.9
+        id: python
+        uses: actions/setup-python@v2
+        with:
+          python-version: 3.9
+
+      # This step caches our Python dependencies. To make sure we
+      # only restore a cache when the dependencies, the python version and
+      # the runner operating system we create a cache key
+      # that is a composite of those states.
+      # Only when the context is exactly the same, we will restore the cache.
+      - name: Restore pip cache
+        uses: actions/cache@v2
+        with:
+          path: ${{ env.PIP_CACHE_DIR }}
+          key: "python-0-${{ runner.os }}-\
+          ${{ steps.python.outputs.python-version }}-\
+          ${{ hashFiles('./requirements.txt', './requirements-dev.txt') }}"
+
+      - name: Install dependencies
+        run: |
+          pip install -r requirements.txt
+          pip install -r requirements-dev.txt
+
+      # Run flake8 and have it format the linting errors in the format of
+      # the GitHub Workflow command to register error annotations. This
+      # means that our flake8 output is automatically added as an error
+      # annotation to both the run result and in the "Files" tab of a
+      # pull request.
+      #
+      # Format used:
+      # ::error file={filename},line={line},col={col}::{message}
+      - name: Run flake8
+        run: "flake8 \
+        --format='::error file=%(path)s,line=%(row)d,col=%(col)d::[flake8] %(code)s: %(text)s'"

requirements-dev.txt

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+flake8~=3.8.4
+flake8-annotations~=2.4.1
+flake8-bugbear~=20.1.4
+flake8-docstrings~=1.5.0
+flake8-import-order~=0.18.1
+flake8-string-format~=0.3.0
+flake8-tidy-imports~=4.1.0
+flake8-todo~=0.7
+pep8-naming~=0.11.1