[WIP] Add NetCDF topography capability

This PR develops the ability to read in topography data in a NetCDF file of the sort GEBCO uses.  I am not completely sure if this a universal format but it works on test data so far.  Currently the biggest question is whether we want to include the pre-processor directives in the file or have a duplicate `topo_module` source that includes the NetCDF.  I favor the former approach but am open to discussion.  It should be noted that by changing the file suffix to `F90` that gfortran should automatically call the pre-processor.