Added more field to exif extractor
I have attached a patch that adds some more fields to the Exif extractor. I also added tests for each field, which all pass on my machine. I hope I did things correctly. If you like it, I would be glad to add more.
The thing that I am unsure about is the quality values in the hachoir-metadata/register.py file. Feel free to tweak those if you wish. Please let me know how I did.