Fix package score in pub.dev

[gbassisp]

Creating this PR to improve its score in pub.dev by applying the following changes:

1. Removing usage of dynamic types, which was causing a warning on the equality operator
2. Adding doc comments on public members of the API
3. Making some members private. I believe they were exposed to the API by mistake
4. Updating the lints dev dependency. This is not a breaking change because dev deps are not carried over to consumers of this package
5. Enabled public_member_api_docs to avoid future problems
6. Marked Dart 3 supported on pubspec
7. Added a bare minimal example

Note: even though I removed public members (see number 3), I bumped the version from 0.5 to 0.6, which is considered a major upgrade (breaking changes allowed)