JGCRI/tethys: Tethys v1.2.0

This release includes the following bug fixes and performance improvements:

• Set GMIA_cropland.csv file in the correct units of square kilometers
• Replace depreciated Pandas methods
• Removed old version GCAM databases from example inputs
• Added GCAM database for reference case from version 5.1
• Removed old test case outputs
• Ran new GCAM 5.1 case outputs
• Updated config file with new database name, replacing temporal climate MAT files with NPZ
• Updated setup.py to new version
• Replaced dependency of MAT files for temporal downscaling
• Notify users of future Python 2 depreciation