Export `as_opt_<type>` helper functions

[rnag]

Closes #4

[rnag]

There seems to be some differing assumptions on what should be None and what shouldn't.

I find the examples section hard to read. Rather than having many examples, it may be better to have unit tests - and examples (doc tests) in src/de_impl_opt.rs doc strings.

Hi @corneliusroemer ! Thanks for bringing this up. I totally agree, that at some point it would be worth it to refactor it to move example cases into doc tests & unit tests more explicitly, that way it also runs automatically in the GitHub Actions workflow (CI) and also when deploying new versions.

I've created a new issue to track effort on this separately, as part of #7 .

For now, as and when when time allows, please take a look at recent changes and commits I have added as part of this PR, to confirm if it resolves or addresses all issues based on your notes. I will hold off on merging the changes until then.

Thanks, and have a great Monday 🎉 !

[josephwynn-sc]

I just stumbled upon this crate and the first thing I wanted was as_opt_* - is there a chance this PR would be merged in the near future?