Support EXIF flipping as well

[fwenzel]

We currently only do rotation (which is, by far, the most frequent case). EXIF also allows flipping though. In fact, I could imagine that's used by front-facing phone cameras?

Pretty easy for us to support.

[fwenzel]

This was a suggestion inside Issue #5.

[fwenzel]

I actually can't find a real-life example of a file that is mirrored. Anyone know if any phone/camera even does that (creating mirrored files)?

[tlhackque]

Well, there's http://elinux.org/Rpi_Camera_Module -hf and -vf

I'm not up-to-date on the commercial cameras, but I'm surprised if none do this. Lots of people seem to take pictures in a mirror; that's one case. Or consider making a T shirt.

In any case, I have received files that had the flipped orientation tags quite a while ago. Doesn't appear that I still have them.

exiftool can be used to create test cases.