Incorporate best practices from the Library Authors' Guidelines

There are certain best practices listed in our official [Library Author's Guidelines](https://kotlinlang.org/docs/api-guidelines-introduction.html).

Those include using:
- `explicitApi()`
- binary compatibility validator
- writing documentation and samples, and using Dokka to render it

It would be nice to incorporate at least some of these practices to help developers creating production-quality libraries right of the bat.

Start with the linked Library Authors' Guidelines and inspect the template's build configuration and documentation setup. Determine which of explicitApi(), the binary compatibility validator, documentation, samples, and Dokka are appropriate to incorporate; done means the selected practices are enabled and usable by developers creating libraries.

Written by the indexing model from the issue text.