Convert to use poetry & pyproject.toml for dep & build management (#54)

* Convert to use poetry and pyproject.toml, update README

* add some resources for contributors

* minor adjustments

* ci: separate tests from linting, run using poetry

* add pytest-mock to dev requirements

* combine running tests and reporting to codecov

* generate both xml and html coverage reports

* add codecov to dev dependencies

kasa/tests/test_fixtures.py

@@ -2,7 +2,7 @@ import asyncio
 from datetime import datetime
 from unittest.mock import patch
 
-import pytest
+import pytest  # type: ignore # https://github.com/pytest-dev/pytest/issues/3342
 
 from kasa import DeviceType, SmartDeviceException, SmartStrip