Humanreadable

- Add `to_humanreadable` method to `BitsPerSecond` class
- Fix `to_humanreadable` method failed when the value is over 1 day: 2 (Thanks to giobri)
- Fix `__all__` in `__init__.py`
- Drop support for Python 3.6
- Improve type annotations
- Modify to use `pypa/build` for package build
- Update `[build-system]`

**Full Changelog**: https://github.com/thombashi/humanreadable/compare/v0.3.0...v0.4.0

- Add additional formats support for `BitPerSecond` class
- Add `__add__` method to `BitPerSecond` and `Time` classes
- Add `BitsPerSecond` class that is an alias of the `BitPerSecond` class
- Add `to_humanreadable` method to the `Time` class

- Add support for Python 3.10/3.11
- Drop support for Python 3.5
- Change `BitPerSecond.bps` property type from `int` to `float`
- Add type annotations
- Update requirements

**Full Changelog**: https://github.com/thombashi/humanreadable/compare/v0.1.0...v0.2.0