Update gexiv2-dump tool
- Prevent incompatibilities with old version by renaming to gexiv2-tool.
- Only processes a single image file
- Replace from_stream() with open_path(), as from_stream() only works with .jpg
- Add options to print different combinations of tags to screen
- Add option to output information about a tag (e.g. description, etc)
- Add option to output Xmp namespace values