Add support for Points features

[eldobbins]

https://www.nodc.noaa.gov/data/formats/netcdf/v2.0/ lists a Point feature type. Its description is:

point | A single data point (having no implied coordinate relationship to other points). | One or more recorded observations that have no temporal or spatial relationship (where each observation equals one point in time and space).

A use case would be x,y,z bathymetry measurements that are intended to go into a grid interpolation, where the x,y are originally scattered around and the measurement times were not recorded.

A resulting netCDF file would look like: https://www.nodc.noaa.gov/data/formats/netcdf/v2.0/point.cdl