Drop Py37, improve typing and docstrings (#544)

Drops Py3.7, improves typing and adds a mypy config, improves the docstrings and isorts the imports.

* configure isort
* sort with isort
* add github action
* enable flake8-docstrings
* fix docstrings
* add mypy env
* no implicit optional
* add type for raw
* add some type hints

.github/workflows/pythonpackage.yml

@@ -30,6 +30,11 @@ jobs:
         python -m pip install --upgrade pip
         pip install flake8 pytest tox tox-gh-actions
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
+    - name: Check sorting of imports
+      uses: isort/isort-action@master
+      with:
+        requirementsFiles: "requirements.txt doc/requirements.txt"
+        sortPaths: "./doc ./src ./examples ./test ./setup.py"
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names
@@ -50,4 +55,4 @@ jobs:
         files: ./coverage.xml,!./cache
         flags: unittests
         name: coverage-tox-${{ matrix.python-version }}
-        verbose: true
+        verbose: true