Add tox environment for building and checking distributions

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 # When adding a new Python version here, please also update the list of Python versions called by the GitHub Actions workflow (.github/workflows/ci.yml).
-envlist = py{36,37,38},flake8,mypy
+envlist = py{36,37,38},flake8,mypy,package
 
 [testenv]
 commands = python -m unittest discover --start-directory ./tests
@@ -16,3 +16,12 @@ commands = flake8
 deps =
 	mypy
 commands = mypy
+
+[testenv:package]
+deps =
+	twine
+	wheel
+
+commands =
+	python setup.py sdist bdist_wheel
+	twine check dist/*