Add __version__ attribute to package

tests/test_version.py

@@ -0,0 +1,13 @@
+from betterproto import __version__
+from pathlib import Path
+import toml
+
+PROJECT_TOML = Path(__file__).joinpath("..", "..", "pyproject.toml").resolve()
+
+
+def test_version():
+    with PROJECT_TOML.open() as toml_file:
+        project_config = toml.load(toml_file)
+    assert (
+        __version__ == project_config["tool"]["poetry"]["version"]
+    ), "Project version should match in package and package config"