SOSE-derived Weddell gyre data, reworked for use with xWMB

Light-weight datasets derived from SOSE (https://sose.ucsd.edu/) data, broadly corresponding to the Weddell gyre, and for January and March 2013 monthly means. These datasets contain all the terms needed to close the mass, heat and salt budgets, with diagnostics reworked so as to be usable directly with xWMB (https://github.com/hdrake/xwmb).