Initial vLLM-omni repository structure

- Add complete directory structure for multimodal and non-autoregressive processing
- Include AsyncLLM, OmniEngine, and DiffusionEngine modules
- Add processors, schedulers, executors, and output processors
- Add API interfaces for Higress, Gradio, and ComfyUI
- Add configuration management and CLI interface
- Add comprehensive test structure and documentation
- Add pyproject.toml with dependencies and project configuration
- Add examples and documentation structure

docs/README.md

@@ -0,0 +1,5 @@
+# vLLM-omni Documentation
+
+Welcome to the vLLM-omni documentation! This documentation provides comprehensive information about using and developing with vLLM-omni.
+
+# TODO (add examples)