Return original filename

I want the original filename so I can show it in my app. I am not 100% sure if we should give it a better name like `original_filename` (that seems to be what I'm calling it and some other libraries use it IIRC). 

How do you feel about switching the tests to use real fixture files so we can assert the file size and file name better? Right now the filename ends up being a random tempfile name so I can just match the beginning.