I18nice

- Added flake8 and mypy checks
- Enabled and ensured branch coverage
- Added `__all__` to packages
- Added more type hints
- Fixed static references not expanding
- Fixed strict pluralization with translation tuples
- Created `dev-helper.py` for pre-commit and GA
- Made `PythonLoader` throw more verbose error

- (pb) `i18n.get("filename_format")` will return `FilenameFormat` instead of string. You can access `template` attribute to get the original string. `set` will continue to work as usual.
- More flexible filename formats
- Type hints for public APIs
- New functions `load_everything` and `unload_everything`
- 100% coverage
- Minor optimizations

- Added static references feature
- Added full translation list support

- Added PyPI publishing

Note: versions listed below aren't available on PyPI

- (pb) Switched to `yaml.BaseLoader`

- Improved memoization (again)