Create unit tests for ocean_merge code

[GeorgeGayno-NOAA]

Follow the procedures used in other programs:

• Place the 'guts' of the program into Fortran modules that are accessed by a simple driver.
• Modify build to create a library that is linked by the driver.
• Create unit tests that link to the library.

Unit tests should be created for all major functions of the code:

• The read of the orography file.
• The read of the namelist file.
• The loop that merges the land and ocean masks along coastlines.
• The write of the updated orography file.