Link between Reference pages and Examples pages

[omnikrll]

For instance:

The reference page for the normalMaterial() method (https://p5js.org/reference/#/p5/normalMaterial) includes a simple snippet of example code, but does not include any links to the Materials example page (https://p5js.org/examples/examples/3D_Materials.php). Conversely, the Materials example shows calls to the texture(), basicMaterial(), normalMaterial(), ambientMaterial(), and speculatMaterial() methods, but there are no links to the reference pages for those methods.

In my experience, this kind of separation between reference and examples led me to open the Reference and Example pages for certain methods in different tabs, which led to a lot of tab clutter.

[lmccart]

https://github.com/processing/p5.js/commit/4c2ada1fe80c954e9bcdad3d5e9d2b056ce70492