Emissions changes in 2020 due to Covid19

Version 4 has smoother treatment of oceans, using a global value for locations not overlapping with the coast of a country (coastal locations us the country-specific modifiers). From Version 2, more years are provided via interpolation. The baseline data is also provided for convenience and interpolated onto same years. There is also a bug fix for the aerosol precursor files that affected July 2020-Dec 2021