#6 - coupler_unpack_ocean_ice_boundary, coupler_exchange_slow/fast_ice, coupler_set_ice_surface_fields

[mlee03]

In this PR, the following coupler subroutines are defined and are called in full coupler_main

1. coupler_unpack_ocean_ice_boundary,
2. coupler_exchange_slow_to_fast_ice,
3. coupler_exchange_fast_to_slow_ice, and
4. coupler_set_ice_surface_fields

Subroutine coupler_unpack_ocean_ice_boundary calls both flux_ocean_to_ice_finish and unpack_ocean_ice_boundary.

Subroutine coupler_exchange_fast_to_slow_ice contains an optional argument to set the current pelist to Ice%pelist. This subroutine is called twice in coupler_main where only the second call requires the setting of the current pelist.

[thomas-robinson]

Please add some more documentatiion for the subroutine descriptions. It will be helpful in any of the automated documentation generation to have more details about the subroutines