todo list

- Allow access to the tag values using the dictionary syntax (read values on the fly when needed, lazy instantiation) -> operator overloading with __getitem__() and __setitem__()
- Also allow the deletion of items in the same way
- Cache already queried values (see dictionary on previous line)
- Disable the get...() and set...() methods (by making them private) -> metadata is accessible only through the dictionnary metaphor
- Rewrite the exiv2 command-line tool and the test binaries in Python and (Python) scripts to run the same tests that are run to test exiv2
- Write a complete documentation for the binding and it uses