Backoff

Added
- Add raise_on_giveup keyword arg for decorators
- Add backoff.runtime wait generator for dynamically setting wait times based
on target function return value or exception details
Changed
- Improve type hints for on_success, on_backoff, on_giveup handlers
- Use decorator-specific detail and handler type hints
- Optionally use typing_extensions for python 3.7 type hinting
- Drop python 3.6 support
- Add python 3.10 support

Fixed
- Update __version__ in backoff module

Added
- Configurable logging levels for backoff and giveup events
Changed
- Minor documentation fixes

Changed
- Allow sync decorator call from async function
- NOTE: THIS WILL BE THE FINAL PYTHON 2.7 COMPATIBLE RELEASE.

Changed
- Don't include tests and changelog in distribution

Changed
- Include tests and changelog in distribution