0.2.0 alpha 1

Documentation update

- Fixed some typos in the documentation
- Added reminders for common compatibility issues with dirmod

Project restructure

Fixed typos in main description

Updated docs links

Improved documentation

- Added tests
- Rewritten main docs

Initial version

Supports `all!`, `os!`, `family!` and `feature!`.

Supports `default` or specific custom visibility and custom re-exports.

Supports custom none-included error message.

Supports `except`.