added add_data to UGrid class for working with the data associated with teh onde,s edges, etc..

still to do: add writting that to the file...
added writting associated data

plus a bunch of clean-up of the code
bunch more writting code for data attributes, etc.
Added DataSet Object, and code to write datasets to the netcdff file.
Also lots of code for automatically wirting the correct attributes to
reference the grid, and only write what is there.

Still to do: file reading code, ideally lazy-referencing the underlying netCDF4
variables.