Scrapemeagain

Use [`ThreadPoolExecutor`](https://docs.python.org/dev/library/concurrent.futures.htmlthreadpoolexecutor) in favor of `multiprocessing.Pool` for async requests.

Fix sdist by including package files.

- make Dockerfile smaller
- use Jijna2 template for docker-compose.yml

Fix installing dependencies.

ScrapeMeAgain available as a package on PYPI.