Add scale! (non-allocating)
Improve the type-specificity of Overlays
Major refactoring of uint32color

This appears to handle the nest of possible subarrays/overlays/other
weird array types better than previous efforts. It also yields fast
performance for arbitrary dimensions, thanks to Cartesian.
Clean up named->dimension conversion and support size(img, "x")

This also fixes what might have been an undetected bug,
incorrect indexing in images where color is an early dimension.
Add a sleep() to allow writing to finish before testing via read

I was getting ImageMagick library errors on some systems