Deprecation of WP Feature API in favor of Abilities API

[Jameswlepage]

We are beginning the deprecation process for this repository.

The Abilities API project has reached stability, and with WordPress Core 6.9 introducing it as a core feature, this plugin is no longer needed as a long-term standalone solution.

Next steps:

• Users are encouraged to migrate to Abilities API.
• This repository will remain public and eventually be archived for reference.
• No further feature development will take place here.

We thank all contributors and users of the Feature API. The transition to Abilities API provides a more unified and sustainable path forward.