Backrefs

- **NEW**: Significant improvements to Unicode handling. A lot of testing was implemented to catch existing bugs and to improve result.
- **NEW**: POSIX style properties now handle all existing Unicode properties.
- **NEW**: POSIX properties now follow the [Unicode specification for POSIX compatibility][unicode-posix]. Read the [documentation](../refs.mdposix-style-properties) to learn more.
- **NEW**: Unicode properties are now sensitive to the `ASCII` flag and will properly restrict the range of properties to the ASCII range even in Unicode strings.
- **NEW**: Removed the old deprecated search references: `\l`, `\L`, `\c`, and `\C`. These are available in various other forms: `[[:lower:]]`, `\p{lower}`, etc.
- **NEW**: To reduce conflicts of naming, Binary properties are evaluated before Block properties when using short names. Block has conflicts with some other properties of various types, using short names for blocks is discouraged.
- **FIX**: Numerous fixes to existing Unicode properties: missing values, incorrect values, etc.

- **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.