Implement multi-threaded async file and socket operations with pthread-based worker pool, add double floating-point type with conversion and arithmetic functions, introduce file I/O system with fopen/fclose/fread/fwrite/fgets/fputs, and add break/continue control flow statements. Update Makefile with new test and example targets, extend README and TUTORIAL.md with comprehensive documentation and usage examples, and include async_demo.rc example and async_io_test.rc test suite.
