sod 激波管问题的简单实现，包括weno3和weno5，makefile可正常运行，方便使用(Sod shock tube simple implementation of the problem, including weno3 and weno5, makefile can be normal operation, easy to use)

weno3阶格式求解一维黎曼问题，希望大家一起讨论共同学习，仅供参考，有详细的注释(One dimensional Riemann problem, I hope you can discuss and learn together, for reference only, there are detailed notes)