MIL-012: version 0.2.0, CHANGELOG and links

Version 0.2.0 in pyproject.toml, flash_card.__version__ and the Doxyfile
with a test that keeps the three equal; CHANGELOG entry for 0.2.0; README
and the wiki Install pages link the release pages. The upload limit probe
refused a 1 MB file (413), so the executable is not attached. Review
record RC-071 (Go).

Task: MIL-012#2
Task: MIL-012#3
Task: MIL-012#4
Task: MIL-012#8

tests/unit/test_version.py

@@ -0,0 +1,35 @@
+"""Keep the version declared in code, pyproject.toml and the Doxyfile in step.
+
+@file test_version.py
+@brief Unit tests that the three version declarations cannot drift.
+"""
+
+import re
+import tomllib
+
+import flash_card
+from flash_card.constants import PROJECT_ROOT
+
+_SEMVER_PATTERN = re.compile(r"^\d+\.\d+\.\d+$")
+_PROJECT_NUMBER_PATTERN = re.compile(r"^PROJECT_NUMBER\s*=\s*(\S+)\s*$", re.MULTILINE)
+
+
+def _pyproject_version() -> str:
+    with (PROJECT_ROOT / "pyproject.toml").open("rb") as file:
+        version: str = tomllib.load(file)["project"]["version"]
+    return version
+
+
+def test_version_matches_package_version_when_read_from_pyproject() -> None:
+    assert _pyproject_version() == flash_card.__version__
+
+
+def test_version_has_major_minor_patch_form() -> None:
+    assert _SEMVER_PATTERN.match(flash_card.__version__) is not None
+
+
+def test_version_matches_doxyfile_project_number() -> None:
+    text = (PROJECT_ROOT / "Doxyfile").read_text(encoding="utf-8")
+    match = _PROJECT_NUMBER_PATTERN.search(text)
+    assert match is not None
+    assert match.group(1) == flash_card.__version__