Add transpose and speedup rotation

This adds new `Imaging.TRANSPOSE` method for `Image.transpose()` operation. Also this speeds up `Image.ROTATE_90` and `Image.ROTATE_270`.

Method | Before | After
-------|--------|------
**Large 5120x2880 image** |
Flip left right | 0.02635   | 0.0262   
Flip top bottom | 0.01105   | 0.011    
Rotate 90       | 0.3706    | 0.04535  
Rotate 180      | 0.02968   | 0.02933  
Rotate 270      | 0.3786    | 0.04542  
Transpose       |           | 0.04404  
**Small 586x387 image** |
Flip left right | 0.0003951 | 0.0003891
Flip top bottom | 0.0001121 | 0.000108 
Rotate 90       | 0.000602  | 0.000457 
Rotate 180      | 0.000464  | 0.000463 
Rotate 270      | 0.0005708 | 0.0004828
Transpose       |           | 0.0004091


As you can see, this doesn't improve performance for relatively small images, because they whole fit in cache, but for large images this gives 8x speedup.

Tests pending.