Refine the syntax section of the reference

The syntax section of the reference could be clearer in a few places.

Methods

The reference pages for methods such as p5.Vector.add() display the following syntax:

add(x, [y], [z])

add(value)

add(v1, v2, [target])

It'd be helpful to demonstrate the dot operator, and to distinguish between instance and static methods. I suggest standardizing on p5.X.method() and myX.method(), as in:

myVector.add(x, [y], [z]);

myVector.add(value);

p5.Vector.add(v1, v2, [target]);

Side note: I'm not sure whether we should encourage copy/pasting syntax snippets.

Events and Structure

The reference pages for event functions such as doubleClicked() display the following syntax:

doubleClicked([event])

It'd be helpful to demonstrate that these functions are declared, not called, as in:

function doubleClicked([event]) {
  // Code to run.
}

🤦🏽‍♂️ I just noticed that the code snippets for these are broken and will make a pull request soon!

Start with the linked p5.Vector.add() and doubleClicked() reference pages, then inspect how their syntax examples are produced. Done means method examples show instance and static forms with the dot operator, while event examples show declaration syntax rather than calls; resolve whether the snippets should be copyable as part of the same review.