TiffIO: Allow bottom left origin for images

[zm711]

Fixes #876.

I added in a note (in the docstring) explaining that upper left is the python default (from PIL and pillow). As a default I left the upper left, but if the user sets a new argument python_image_origin=False, then it will do bottom left. I agree that upper left is weird, but it is what the python world expects, so I think the boolean is fair (python standard vs other standard).

1. I don't love the name I came up with of python_image_origin so if someone has a better name let me know.
2. I only did a boolean, ie 2 choices, but I guess we could do more complicated, but I think all that flipping is dangerous.

[zm711]

Meeting discussion: string parsing vs boolean for setting bottom-left vs top-left.

[zm711]

@apdavison I think you're best to review this, but if you think someone else is better just let me know. This is done now so you can review and merge whenever you want (or at our next meeting--no rush).