Validate input for brush name

[Ethspresso]

Using brush.set() to set the brush to an unknown string value like a brush name with a typo in it, raises TypeError: Cannot read properties of undefined (reading 'param')

Expected result: An error message saying this is not a valid brush name.

Tested using the non-minified v1.0.3 in the p5js.org editor.

[acamposuribe]

Hi!
I've included error messages for several functions, but only for the full version
The minified version avoids these messages to compress the code as much as possible