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

tox.ini

@@ -22,8 +22,9 @@ deps = jaconv
        pytest-mock
        hypothesis>4
        python-barcode
-commands = pytest --cov escpos --cov-report=xml
+commands = pytest
 passenv = ESCPOS_CAPABILITIES_PICKLE_DIR, ESCPOS_CAPABILITIES_FILE, CI, TRAVIS, TRAVIS_*, APPVEYOR, APPVEYOR_*, CODECOV_*
+setenv = PY_IGNORE_IMPORTMISMATCH=1
 
 [testenv:docs]
 basepython = python
@@ -39,7 +40,16 @@ commands = sphinx-build -W -b html -d {envtmpdir}/doctrees .  {envtmpdir}/html
 
 [testenv:flake8]
 basepython = python
-# TODO add flake8-future
-# TODO add flake8-docstrings
 deps = flake8
+       flake8-docstrings
 commands = flake8
+
+[testenv:mypy]
+basepython = python
+deps = mypy
+       types-six
+       types-PyYAML
+       types-appdirs
+       types-Pillow
+       jaconv
+commands = mypy src