Aiostream

- Properly expose pipe methods in `aiostream.pipe` (PR 88, issue 87)

- Expose `pipable_operator` at package level (46ddb24)
- Modernize examples (a704e9a)

- Drop python 3.7 support
- Add type annotations (issue 36, PR 84)
- Add task_limit argument to action operator (issue 85, PR 86)

Build and upload a wheel package to PyPI

- Fix confusing traceback when calling wait_stream on a empty stream (issue 76, PR 77)
- Add support for python 3.10 and drop python 3.6 (issue 79, PR 80)

- Fix several issues with the task group (issue 73, PR 75)
- Fix "Task exception was never retrieved" warning (issue 71, PR 72)