Migrate the 'annotate()' function to use Annotation object (and upgrade all calls to the annotate() function accordingly)

The function Annotation.__getitem__() return None either if the variable is not found, or the index of the variable is not found

Use the function Annotation.__getattr__() instead of getting the data directly from Annotation_data (return 'None' if the field does not exist, instead of raising an error)

Change the 'zip()' function to 'izip()', to add None values if the format is longer than the data provided

Add a 'clean' parameter to the NIST_MDD().get_pairing() function, to delete the minutiae with no pairing information

'export_latent()', 'export_print()', 'export_latent_annotated()' and 'export_print_annotated()' : Check if the file have been written to disk, and return the value