T21.nc (or equivalent if using a higher resolution--provide your own
though), and randomly generates continents according to the user's
desired number of landmasses and land fraction. It's much better at
getting the land fraction right than the number of landmasses, since
as they grow landmasses often merge. Also generates template
topography (higher elevation at landmass center, no mountains), and
writes SRA boundary condition files for land-sea mask and orography.
