Release Preparation:
- Bumped version from 0.15.0-rc.7 to 0.15.0 (stable release)
- Updated workspace dependencies to use 0.15.0

Documentation Enhancements:
1. **Version Updates**: Changed all version references from 0.15.0-rc to 0.15.0
2. **Enhanced Plugin Examples**: Added comprehensive plugin usage examples:
   - Basic plugin registration with rmqtt-plugins meta-package
   - Programmatic configuration with plugins_config_map_add()
   - Individual plugin dependency approach

3. **New Examples**: Added two new plugin configuration patterns:
   - Using rmqtt-plugins with "full" feature
   - Programmatic ACL rule configuration

4. **Example Improvements**:
   - Simplified logging in plugin example (env_logger → simple_logger)
   - Cleaned up main.rs with better commenting
   - Updated Cargo.toml dependencies

5. **Library Integration**: Enhanced documentation to showcase:
   - Multiple integration approaches
   - Flexible configuration options
   - Real-world usage patterns

Key Changes:
- **Stable Release**: Marked 0.15.0 as production-ready
- **Better Examples**: More practical, copy-paste ready code samples
- **Modernized Tooling**: Updated to current best practices
- **Comprehensive Coverage**: Showcased all plugin integration methods

The changes provide a solid foundation for the 0.15.0 release with improved documentation and examples for developers.