"native" numpy integration

[shadoxxhd]

This integration includes some breaking changes to the existing substrip interface, which to me seem more natural. If minimally disruptive numpy integration was preferred, my "substrip2" branch might be better suited (if desired, I'll make a pull request for that one).

[shadoxxhd]

breaking changes:

• __getitem__ returns numpy arrays instead of lists for slice indices
• getPixels returns a numpy view (reference) to the LED data, instead of a copied list
• createPixelSubStrip uses slice()-like arguments, instead of start,stop,num (or a passed slice object)
• the PixelSubStrip constructor only takes slice objects as substrip extent specification, and offloads index validation to numpy, resulting in different Exception strings
• getPixelColor* functions return numpy arrays instead of lists for slice indices

the substrip2 branch also returns numpy arrays instead of lists, but keeps the original arguments/validation logic of the PixelSubStrip constructor, but that could be trivially reverted with return type checks/conversions

[shadoxxhd]

compared to my original pull request, this is based on your force-pushed changes