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

.pre-commit-config.yaml

@@ -26,11 +26,11 @@ repos:
   - id: flake8
     additional_dependencies: [flake8-docstrings]
 
-
 - repo: https://github.com/pre-commit/mirrors-isort
   rev: v4.3.21
   hooks:
   - id: isort
+    additional_dependencies: [toml]
 
 - repo: https://github.com/pre-commit/mirrors-mypy
   rev: v0.740