Document the 3.0 driver API

[JanJakes]

Summary

This PR prepares the repository's documentation and non-functional metadata for the 3.0 release:

• Driver documentation: Adds a focused package README covering the overview, requirements, usage, DSN format, connection options, compatibility limits, and development workflow. It also documents the public exception and driver accessor in source.
• Package status and naming: Marks the MySQL proxy as experimental and replaces the stale "WP SQLite Driver" name with "MySQL on SQLite."
• Release and source documentation: Corrects the release command and branch naming, outdated option and drop-in metadata, inaccurate class documentation, and spelling and grammar errors.
• Obsolete annotations: Removes @since and @package annotations throughout the repository.

Why

Version 3.0 establishes a well-defined PDO-compatible API. Documenting its entry points, connection format, configuration, and limitations makes that contract discoverable outside source docblocks, while the remaining cleanup removes stale or misleading information before the release is tagged.

These changes do not alter runtime behavior.