[p5.strands] Reduce boilerplate in creating shaders using strands

[davepagurek]

Increasing access

While I think we've made great progress in making shaders easier for newcomers to write, there are a few more things that I think are still relatively complex new constructs that are less common in the rest of p5 that users are exposed to all at once. If we can sand these edges down a bit, it will make p5.strands an even smaller step from non-shader p5.js.

Most appropriate sub-area of p5.js?

• Accessibility
• Color
• Core/Environment/Rendering
• Data
• DOM
• Events
• Image
• IO
• Math
• Typography
• Utilities
• WebGL
• Build process
• Unit testing
• Internationalization
• Friendly errors
• Other (specify if possible)

Feature enhancement details

I've made two sub-issues with two problems/suggested changes for these. (Also let me know what you all think of sub issues, if those help with organization or make it messier!)