GFisher 0.2.1

• New maintainer: Zheyang Wu (zheyangwu@wpi.edu).
• The package now has a public repository and issue tracker: https://github.com/ZWuLab/GFisher. Added Authors@R, URL, and BugReports fields to DESCRIPTION.
• The reference in Description now points to the published paper (Zhang and Wu, 2022, Biometrics, doi:10.1111/biom.13634) instead of the arXiv preprint.
• No changes to functions or computations.