Futurepool

* Add PyPi badge to README
* Move to `asyncio.Semaphore` and use locks on shared resources
* Fix issue with async iterator stop condition

**Full Changelog**: https://github.com/MichalKarol/futurepool/compare/1.0.0...1.0.1

Initial release of FuturePool. :partying_face:
Basic functionalities are covered with tests and PyPi package is offically published.