Implement "-atmosphere one_station" in 0.6.

This atmosphere model reads scalar time-series of the near surface air
temperature and precipitation and uses them at all grid points in the
domain. Resulting climate fields are constant in time *unless* a
modifier such as lapse_rate is used to create spatial variability.

Use "-atmosphere_one_station_file" to specify the name of the file
containing "air_temp" and "precipitation" variables.