v0.4.0

This release improved the process and the features required for ONNXRuntime Mobile and ONNXRuntime Web,
Specifically

1. Support Android/Web-Assembly build
2. Support the custom build for the selected operators
3. Support non-exception C++ build
4. Add mobile-optimized operators for string manipulation and tokenization
5. The GPT-2 beam search tool
6. Some bug fixings