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

examples/docker-flask/app.py

@@ -1,12 +1,15 @@
-from escpos.printer import CupsPrinter
+"""Example for a flask application."""
 from flask import Flask
 
+from escpos.printer import CupsPrinter
+
 # Initialize Flask app
 app = Flask(__name__)
 
 
 @app.route("/", methods=["GET"])
 def do_print():
+    """Print."""
     # p = Usb(0x04b8, 0x0e28, 0)
     p = CupsPrinter(host="localhost", port=631, printer_name="TM-T20III")
     p.text("Hello World\n")

examples/docker-flask/requirements.txt

@@ -3,7 +3,6 @@ argcomplete==3.0.8
 blinker==1.6.2
 click==8.1.3
 Flask==2.3.2
-future==0.18.3
 itsdangerous==2.1.2
 Jinja2==3.1.2
 MarkupSafe==2.1.2