Support reading signed 8-bit TIFF images

[radarhere]

Resolves #811 using the suggested code.

Test image was created with a modified Pillow.

[hugovk]

Let's add this to the release notes.

[radarhere]

This is not completely simple, because there are a variety of specific settings in OPEN_INFO.

I've adjusted the code to also support both ByteOrders, and presumed that I don't need to mention that there aren't any ExtraSamples supported and that FillOrder 2 isn't supported since "FillOrder=2 is not required in Baseline TIFF compliant readers".

So the release notes read

Support reading signed 8-bit TIFF images
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

TIFF images with signed integer data, 8 bits per sample and a photometric interpretaton of BlackIsZero can now be read.