Hijridate

This version has more accurate conversion and better internal code. Details are as follows:

- Dropped support for the years before 1343 AH because the Umm al-Qura calendar was not established then.
- Added `validate` parameter to Hijri class for optional disabling of Hijri date validation and improving performance. However, disabling validation will decrease the conversion accuracy silently.
- Verified conversion against original references and updated the `month_starts` tuple for more accurate conversion.
- Improved `Hijri` class rich comparison methods.
- Improved date validation methods for better performance and readability.
- Made the `Hijri` class hashable by adding a custom `__hash__` method.
- Refactored many internal methods (not affecting the API).
- Other minor fixes, enhancements and performance boost.

In short, this version supports only lunar Hijri calendar on Python 3.6+, and the conversion is in complete agreement with the official Umm al-Qura calendar. Details are as follows:

- Renamed the package to `hijri-converter`.
- Dropped support for the solar Hijri calendar.
- Dropped support for Python 3.5.
- Refactored localization and `ummalqura.py` module.
- Updated `month_starts` tuple in alignment with the Umm al-Qura calendar.
- Added `fromdate()` classmethod to `Gregorian` class.
- Added `notation()` method to `Hijri` and `Gregorian` classes.
- Added more methods to `Gregorian` class including `slashformat()`, `month_name()`, `day_name()` and `to_julian()`.
- Renamed `month_days()` method of `Hijri` class to `month_length()`.
- Changed formatted string to use f-strings.
- Improved documentation and examples.
- Updated unit tests.
- Fixed other minor issues and typos.

- Added `fromisoformat()` classmethod to `Hijri` class.
- Added support for rich comparison between Hijri dates.
- Updated documentation and testing code.
- Other minor fixes and enhancements.

- Refactored conversion methods to improve performance.
- Changed date validation back to be the default and removed optional parameter.
- Added `to_julian()` method to `Hijri` class.
- Updated documentation and testing code.
- Other minor fixes and enhancements.

- Fixed a bug in range validation for the Gregorian date.
- Changed generic typing to built-in types.
- Added more tests to cover the solar calendar.
- Improved code structure and documentation.

- Improved documentation and changelog.