Flowbase

Based on guidance from [Python concurrency with Asyncio](https://www.manning.com/books/python-concurrency-with-asyncio) by Matthew Fowler, this release simplifies the asyncio code, and fixes some warning:

- It makes sure coroutines that were not properly awaited are now awaited.
- It uses `asyncio.create_task()` and `asyncio.run()` instead of manually creating and keeping track of the event loop.

This is a very small change, adding a Port object (subclassing asyncio.Queue), so that the user don't need to import the asyncio library at all, thus making user code cleaner.

This is the first barely working version. See the examples folder for an example that uses the library.