skeleton package

This package can be copied when a new package should be created.

$3

- Adjust "name", "description", and "private" in package.json.
- Put this package into root /package.json "jest.references".
- Put this package into root /tsconfig.json "references".
- Put this package into root /tsconfig.esm.json "references".
- Add dependencies to package.json and run node sync-tsconfig-deps.js to adjust tsconfig automatically.
- Add to .github/workflows/main.yml tsc build step if necessary.
- Add to typedoc build in deepkit-website if necessary.
- Adjust README.md