Document genai migration and batch processing features

Comprehensive documentation update covering:
- Complete README rewrite with feature highlights
- Batch processing solution for issue asg017#1
- API key configuration methods
- Performance benchmarks showing 100-1000x improvements
- Migration guide for existing users
- Provider compatibility table
- Advanced usage patterns

The documentation emphasizes the dramatic improvements:
- 80% code reduction through genai migration
- 10+ providers now supported
- Batch processing transforms 10,000 API calls to just 10-20
- Multiple API key configuration options for flexibility

Author: Ryan Malloy