Add preliminary support for word-swap for odd rows

[mkst]

Opening as draft for comments:

• Not sure if this is the best place to be making the changes
• Not 100% sure if the changes work (I'll try do some testing later this week).
• Not sure if the logic can't be simplified/improved, maybe a better iterator or zip or something to do the swapping.

I also ran the image.py through black which is why its formatted a little different - happy to undo that and recommit separately.

Example swapping a 32-pixel image:

# I4 (8 pixels makes 4 bytes)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15] # orig xrange
[8, 9, 10, 11, 12, 13, 14, 15, 0, 1, 2, 3, 4, 5, 6, 7] # swapped xrange

# I8 (4 pixels makes 4 bytes):
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31]
[4, 5, 6, 7, 0, 1, 2, 3, 12, 13, 14, 15, 8, 9, 10, 11, 20, 21, 22, 23, 16, 17, 18, 19, 28, 29, 30, 31, 24, 25, 26, 27]

# RGBA16 (2 pixels makes 4 bytes):
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62]
[4, 6, 0, 2, 12, 14, 8, 10, 20, 22, 16, 18, 28, 30, 24, 26, 36, 38, 32, 34, 44, 46, 40, 42, 52, 54, 48, 50, 60, 62, 56, 58]

# RGBA32 (1 pixel makes 4 bytes):
[0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 68, 72, 76, 80, 84, 88, 92, 96, 100, 104, 108, 112, 116, 120, 124]
[4, 0, 12, 8, 20, 16, 28, 24, 36, 32, 44, 40, 52, 48, 60, 56, 68, 64, 76, 72, 84, 80, 92, 88, 100, 96, 108, 104, 116, 112, 124, 120]