Document the prototype.valueOf() usage to get pointer from class instance in JS.

[forcepusher]

As seen in this issue, it's not really apparent that we can use the valueOf() method to convert a class view into a pointer. I can't find any references to it in the manual, neither the info that it's being automatically converted into a pointer when using __retain(), __release() methods and such.

[dcodeIO]

Do you have thoughts on where and how to document the behavior ideally?

[forcepusher]

I think somewhere around this area. It could also cover the usage of the new constructor as seen here.
Regarding how exactly to document it - I'm not sure, I've only recently found it myself.
But I think we could just document that same test case.