allow event if targetElement does not exist in the DOM anymore

[fsiliadin]

Hello, I've been working on a bug with an app that uses your library (by the way I have to say it's awesome) and I thought of the following case:

When we are on a popup which displays with a grayout (like a modal) and you click on the grayout to hide the popup (and the grayout of course) and then you click on what was overlayed by the popup, then you have a strange issue: you have to click twice in order to trigger the actual click event. I had a look and it seems like, at the first click after the popup closure, the variable this.targetElement is still refering to the grayout element that actually disappeared from the dom. That's what my second commit tries to fix.
The first commit is just to update the mouseEvent instanciation: https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/initMouseEvent