Unsubscribe when take* completes

[veyh]

In RxJS, take* unsubscribes after onCompleted/onError. In RxLua, it doesn't. I'm not sure if that's intentional or not, but in case it isn't, here's a fix.

[4O4]

I've been digging into this as I wasn't exactly optimistic that this PR is gonna solve all issues for me, and now I can say that it is indeed not enough to properly fix the issue, because the problem is actually a bit deeper.
When the observable emits complete or error it should automatically unsubscribe... at least it does so in rxjs implementation where everything works in a predictable way, but not in RxLua.

I've spent a lot of time comparing these two implementations and I've managed to fix the underlaying issue. I'm gonna send PR in a couple days when I polish things up as I was debugging multiple problems and messed the code up a lot :) But the end result will be proper automatic unsubscription in general (not only for take* operators) which will also work properly with cold observables which complete instantly in a synchronous way. This is important because Observables differ from Promises in that they don't have to be asynchronous and it can be leveraged in quite a lot of use cases.

Anyway thank you for your work on this @veyh because even though it's not a full fix, it helped me a bit to find a right direction while researching this issue :)

[4O4]

Hello, I don't want to send spam but since this is directly related I'll just leave a link to my comment in another issue: #22 (comment)