Definition of a read/write plugin
---------------------------------

All the read/write plugins must provide a python file containing:

    - The characteristics of the IO plugin as the following python variables:

        # Plugin characteristics
        # ----------------------
	    format_name = <String>
        description = <String>
        full_support = <Bool>	# Whether all the Hyperspy features are supported
        # Recognised file extension
        file_extensions = <Tuple of string>
        default_extension = <Int>	# Index of the extension that will be used by default
        # Reading capabilities
        reads_images = <Bool>
        reads_spectrum = <Bool>
        reads_spectrum_image = <Bool>
        # Writing capabilities
        writes_images = <Bool>
        writes_spectrum = <Bool>
        writes_spectrum_image = <Bool>
        # Support for non-uniform axis
        non_uniform_axis = <Bool>

    - A function called file_reader with at least one attribute: filename

    - A function called file_writer with at least two attributes: 
        filename and object2save in that order.

They must also be declared in io.py
