Frozendict

* C Extension is now optional by default
* Pure py package will be no more pubished on Pypi
* Fixed incompatibility with pyinstaller
* Fixed little bug with mypy

**Full Changelog**: https://github.com/Marco-Sulla/python-frozendict/compare/v2.3.4...v2.3.5

* fixed various memory leaks
* Implemented a memory leak tracer

**Full Changelog**: https://github.com/Marco-Sulla/python-frozendict/compare/v2.3.3...v2.3.4

Fixed memory leaks in `repr()` and in costruction of an empty `frozendict`.

**Full Changelog**: https://github.com/Marco-Sulla/python-frozendict/compare/v2.3.2...v2.3.3

Fixed a memory leak in `__hash__()` (thanks to gusostow for the report)

**Full Changelog**: https://github.com/Marco-Sulla/python-frozendict/compare/v2.3.1...v2.3.2

* Added `key([index])`, `value([index])` and `item([index])` methods
* Other internal changes and clean-ups

**Full Changelog**: https://github.com/Marco-Sulla/python-frozendict/compare/v2.3.0...v2.3.1

Added set, delete and setdefault methods.

**Full Changelog**: https://github.com/Marco-Sulla/python-frozendict/compare/v2.2.1...v2.3.0