Mandelbrot set vectorized

Produces the Mandelbrot set, as other user contributed "m" files, but this submission is VECTORIZED, achieving a speedup of approx 2.5 against a traditional implementation (which is optimized by the JIT). In the past (6.0), a vectorized implementation would achieve speedups up to 100 times faster, this is no longer true.
This is a very instructive example of how to vectorize nested loops.

When being used in interactive mode you can zoom into a region of interest and launch again the computation with a GUI push-button.