setup links are incorrectly pointing to python-metar

[austinorr]

All links in our packaging point away from this project towards a dependent project python-metar. The next release will correct this to point to this project instead per standard packaging expectations and pypi links. Users can go find python-metar if they wish, but this project's url should point to this project.

We will continue to credit python-metar extensively throughout our readme, docs, and docstrings.