added graphing 2d equations example

[two-ticks]

Fixes #952

Added Graphing 2D Equations example to http://p5js.org/examples from https://processing.org/examples/

https://editor.p5js.org/radium.scientist/full/t7snmm5qy

[limzykenneth]

@two-ticks Looks good so far. Are you thinking about adding KaTeX equation formatting at this point or is this ready to merged?

[two-ticks]

It is producing same result as processing.org so for now we can consider it to be ready for merge.

[two-ticks]

We can open separate issue for KaTeX equation formatting because other examples such as Sine Cosine also require KaTeX equation formatting.

[lmccart]

can you update this to ES6 and use const or let for these?

[two-ticks]

Changes :

let n = (mouseX * 10.0) / width;
const w = 16.0; // 2D space width
const h = 16.0; // 2D space height
const dx = w / width; // Increment x this amount per pixel
const dy = h / height; // Increment y this amount per pixel
let x = -w / 2; // Start x at -1 * width / 2
let y;

let r;
let theta;
let val;

[lmccart]

can you please update to ES6 in all three files? thanks!

[two-ticks]

updated es6 in all three files

[lmccart]

looks great, thanks!