Add comprehensive API documentation and numpy array verification tests

- Add extensive API documentation in docs/ directory:
  - API_REFERENCE.md: Complete API reference with all methods and types
  - GUIDE.md: Comprehensive user guide with best practices
  - EXAMPLES.md: Practical code examples for various use cases
  - QUICK_REFERENCE.md: Quick reference card for common operations
  - README.md: Documentation index and navigation

- Add test_no_numpy.py: Comprehensive test suite to verify no numpy.ndarray types are returned from any function
  - Tests all CountriesClient methods
  - Tests all IntblocksClient methods
  - Tests all SearchClient methods
  - Includes tests for complex nested data structures
  - All 28 tests pass successfully

Author: ivbeg