if(AntiModals.confirm("Are you sure?")) { ... } doesn't wait for input and always returns true unlike the default confirm("foo")
I don't know if this is a bug or not since the behavior of the modals isn't described anywhere.
You should consider updating your README.

I want to run a function when a modal is closed. I can place a class on close buttons, but what about simply clicking outside the modal?

A readme would be great. More important a LICENSE file is missing, so your code would technically be unredistributable by law in most countries.

DismissOverlay without parameters don't work at all.

Documentation does not state that there should be a need to put parameters mon the dismissOverlay function -- however inspecting the source code it looks like the search for the overlay is broken, but as a workaround providing the DOM object directly makes it work, like

'change input': (evt,f) -> AntiModals.dismissOverlay($(f.firstNode).parent())