Add unit testing to ocean_merge program

[GeorgeGayno-NOAA]

DESCRIPTION OF CHANGES:

Refactor the ocean_merge code into subroutines. Add unit testing.

TESTS CONDUCTED:

If there are changes to the build or source code, the tests below must be conducted. Contact a repository manager if you need assistance.

• Compile branch on all Tier 1 machines using Intel (Orion, Jet, Hera, Hercules and WCOSS2).
• Compile branch on Hera using GNU. Done using aff1a41.
• Compile branch in 'Debug' mode on WCOSS2. Done with no warnings using aff1a41.
• Run unit tests locally on any Tier 1 machine. All tests passed with aff1a41. (Used IntelLLVM on Hercules and Hera; used Gnu on Hera; used Intel Classic on WCOSS2)
• Run grid_gen consistency tests locally on all Tier 1 machines. Done using aff1a41. All passed on Jet, Hera, Hercules, Orion and WCOSS2.

Additional test: the grid_gen consistency tests don't exercise the ocean_merge program, so a C192 grid was created using on Hercules using the script in ./driver_scripts. Output orography files from the branch at aff1a41 and the develop at 122010e were identical.

DEPENDENCIES:

None.

DOCUMENTATION:

The new ocean_merge routines need Doxygen comments.

• Create Doxygen with no warnings due to the ocean_merge code. Done on Hera using aff1a41.

ISSUE:

Fixes #944.