Vectorize example applying iterative function analysis to specific values

[rossbar]

Removes the outer loop over each individual value and instead computes them all at once (the inner loop for applying the function sequentially to previous values is kept). Also condenses the visualization into a single subplot with multiple axes.

[mattip]

Is there a way to preview the result changed tutorial?

[rossbar]

Good question. Here's the:

• original version: https://numpy.org/numpy-tutorials/content/tutorial-plotting-fractals.html
• this PR: https://316-248354526-gh.circle-artifacts.com/0/site/_build/html/content/tutorial-plotting-fractals.html

Unfortunately there isn't really an html anchor anywhere near the proposed change. If you ctrl+f "iterations to each value", the modified code block is the one immediately after that paragraph.

The main goal was to remove the outer for loop and instead use vectorization to do the computations, which I thought might be a better fit for a numpy tutorial. I also ended up modifying the plots, so feedback on the visualization changes welcome.

[melissawm]

Changes look good to me - thanks @rossbar !

[melissawm]

@MichaelRipa want to take a look?

[MichaelRipa]

I like this update, much less wasted space now with the shared colorbar and the 3 plots fitting onto a single row. The code is easier to follow with the outer loop removed, and the plots that were created using the Julia function also look a little less saturated, which is nice. Thanks @rossbar !