Backrefs

- **NEW**: Provide wheels for all officially supported versions of Python.

- **NEW**: Added new back reference `\h` to Re. To get similar functionality with Regex, users must update to the latest Regex release.

- Added the following binary properties for Unicode 13.0 support (Python 3.9): `emoji`, `emojicomponent`,
`emojimodifier`, `emojimodifierbase`, and `emojipresentation`. Associated aliases are also included: `ecomp`, `emod`,
`ebase`, and `epres`.

- **NEW**: Install Regex library along Backrefs via `pip install backrefs[extras]`.
- **NEW**: Remove `version` and `__version__` and remove associated deprecation code.

- **FIX**: Fix Python 3.8 installation issue due to Unicode bundle having an incorrect encoding in some files.

- **NEW**: Deprecate the **search** references `\l`, `\L`, `\c`, and `\C`. The POSIX alternatives (which these were shortcuts for) should be used instead: `[[:lower:]]`, `[[:^lower:]]`, `[:upper:]]`, and `[[:^upper:]]` respectively.
- **NEW**: Formally drop support for Python 3.4.