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

test/test_cli.py

@@ -4,10 +4,12 @@
 
 
 import os
+import shutil
+import tempfile
+
 import pytest
 from scripttest import TestFileEnvironment as TFE
-import tempfile
-import shutil
+
 import escpos
 
 TEST_DIR = tempfile.mkdtemp() + "/cli-test"