Export error sentinels as public

[fudanchii]

Hi, thank you for the project! Wondering if there are some interest in exporting error sentinels as public here. 🙏

I know this was requested at #28 , we also require the sentinel to be public so we can analyze some archives and compare the errors, which otherwise will need to compare the error message directly.

With this change we publish all the sentinels, targeting experimental branch.

I understand if this is not the intended use case, hope we can discuss further on how it's best to analyze rar archive via this package.

Thank you!

[davidnewhall]

Thank you @fudanchii!

• Once merged, this closes #28.

@nwaples I really hope you can give us a few minutes to look over the current pull requests and open issue. <3