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_cli.py

@@ -1,6 +1,6 @@
 import pytest
-
 from asyncclick.testing import CliRunner
+
 from kasa import SmartDevice
 from kasa.cli import alias, brightness, emeter, raw_command, state, sysinfo