fullscreen() switching to windowed mode?

[lee2sman]

Describe the bug
According to the fullscreen() reference page, if you call fullscreen() on an already-fullscreen'ed program then it should "return to its original size." Nope! That isn't actually how it works currently. It just re-switches to fullscreen again. In p5.js, you can call fullscreen(false) to switch to the original size. But Processing was instead targeted. One mistake, in fact, Processing's fullScreen() function uses a capital F but we're using p5's lowercase.

QUESTION: Should we reproduce p5's ability to switch back to windowed? If so, what should be the command?

Possible fixes

1. Correct the L5 reference page for fullscreen() and remove section mentioning you can switch back to windowed mode. (easiest solution but leaves out potentially desired functionality)
2. change L5.lua so that calling fullscreen() a second time switches from fullscreen to window with saved previous dimensions. But maybe this is confusing?
3. imitate p5 and make it so you have to explicitly call fullscreen(false) to switch to windowed mode
4. Something else? If so, what?