DataFrame fixes

Fixes in the joining of DataFrames for individual magnetometers when the time index does not match.

Updates for Pandas 2.0.2 and cdflib 1.0.4

Small modifications to work with Pandas 2.0 and cdflib 1.0

GMAG Frontiers Initial Release

Initial release of the GMAG Python Package.

Includes, loading, downloading, cleaning, and rotating of ground-based magnetometer data from over 200 stations apart of 12 arrays.