rwig 0.1.0

• Initial CRAN submission.
• Efficient implementation of several Optimal Transport algorithms in
  Fangzhou Xie (2025) doi:10.48550/arXiv.2504.08722 and the Wasserstein Index Generation (WIG) model in Fangzhou Xie (2020) doi:10.1016/j.econlet.2019.108874.