Removed unused nc.py module.

Removed
-------
* The nc.py module contained old implementations of netcdf writers.
Change styling to PEP8.
Changed a few remaining stuff to PEP8.
Removed old doctests.
Changed to PEP8 styling.
Fixed failing doctests.

Fixed
----
* Some doctests were failing because we no longer put the variable name in the file name.
Removed redundant bov.py file.

Removed
-------
* Most everything in bov.py is now in bov_io.py.
* bov.py defined the class BovFile but it was unused.
Changed to accommodate an empty vars list.

Changed
-------
* NearestVal mapper can be initialized with an empty list of var names to map. If
  the vars list is empty, then don't pass any var names to the get_x and get_y
  methods of the input grid.
Fixed failing doctests.
Changed for PEP8 styling.
Changed for PEP8 styling.
Changed package name ESMP to ESMF.
Changed to use new ESMPy interface.
Changed to use the bov_io module rather than bov.
Removed unused import of string module.
Changed styling to PEP8.
Changed to use nose rather than unittest.