- use xdoctest to validate code snippets in docstrings
- make xdoctest part of the nox session "test" via
the new `test_docstrings()` test case
- add nox session "test-docstrings" for convenience;
also, `xdoctest.doctest_module()` does not discover
docstrings that are imported at the root of the package
=> each new module with docstrings must be added to
`test_docstrings()` by hand, which is likely forgotten
=> the nox session "test-docstrings" should run on CI
- `lalib.__version__` is dynamically assigned
- the format is "x.y.z[.dev0|aN|bN|rcN|.postM]"
where x, y, z, M, and N are non-negative integers
+ x, y, and z model the "major", "minor", and "patch"
parts of semantic versioning
(See: https://semver.org/#semantic-versioning-200)
+ M is a single digit and N either 1 or 2
=> This complies with (a strict subset of) PEP440
- add unit tests for the `__version__` identifier
- use pytest as the test suite and
measure test coverage with coverage.py
- add package for the test suite under tests/
- add nox session "test" to run the test suite
for all supported Python versions
- use flake8 to lint pytest for consistent style