PyDataArray:_create_data: Extract array writing as writeData
PyDataArray: Export writeData as _write_data
PyDataArray: Add readData and expose ad _read_data
PyDataArray: extract common array check code to make_array
PyDataArray: new array_shape_as_ndsize

Extract common code from readData, writeData
PyDataArray: new array_desc_as_dtype (does type checking)

Like py_dtype_to_nix_dtype() but throws an exception for types
that cannot be handled by NIX
[nix.data_array] Add DataSet object as proxy for data IO

And return the new DataSet object from create_data
[test] DataArray/DataSet: Test write_direct, read_direct
Merge pull request #25 from gicmo/data_io0

Add DataSet and .read_direct, .write_direct methods

Nice