Add Stubfile for better type-hinting support

[Vizonex]

So I found this library when I was going through awesome C's list and I happened to really like duktape for being super lightweight and faster than js2py so I wanted to return the favor by making a stubfile for this library to make it easier for people to use this library. Let me know if there should be any other changes to any of these type-hints that I've added.