Replace exiftool with taglib#

Main reason is that the previous fix for non-ascii characters in filenames, involving pumping the data into standardInput and reading from standardOutput,
was crashing for many (typically larger) images.
The new code is cleaner, shorter, doesn't require starting a new process, backwards compatible, and more likely to be cross-platform.
As a bonus two previously disabled unit tests now pass, and it seems to be picking up more pre-existing metadata.