P5.js: confirm/implement use of Promises across codebase

[lmccart]

This one may already be done, but I'm opening an issue so that we can go through the codebase and confirm that Promises are used for all loadX() methods and anywhere else that a callback is used internally. Additional issues can be opened for areas discovered that require Promise implementation.

[limzykenneth]

Promises are currently polyfilled so considerations can be made about removing the polyfill as well

[ankur54]

Hi. I have found a few code snippets, where callback functions were used instead of promises. I would like to work on this issue.

[dhuang612]

Hi, is this still available to work on?

[lmccart]

@dhuang612 it is!