ObservableType extensions force observeOn calls

[ggrell]

First time looking at the ModelMapper code (Thank You for implementing & sharing it!) I noticed something that is a problem:

The four map* functions contain observeOn calls in the chain. These really shouldn't be applied at this level because a) they cannot be overridden with my own scheduler, and b) should probably be left up to the subscriber (at the Moya call level) to properly observeOn and subscribeOn the correct schedulers.

I'm happy to submit a PR for this change. If not, I'll need to use a fork of the project because of this.

[sunshinejr]

Hey @ggrell, thanks for the issue. When I created this library I wanted to make sure no-one is mapping big objects using main thread. However I see where you coming from so after thinking about it for a little bit I think that I can agree to the change. Having in mind that Moya also added the queue as a parameter for request this is a great follow-up.

Unfortunately this means another major version bump, so I will do an issue for proper Swift 3.0 naming check so we can have everything in the next version altogether. Thanks again! 👊

[sunshinejr]

Damnit. Forgot about that one. Well, let's add it to 6.0.0 because Moya 10.0.0 is nearby anyways. 😄

[sunshinejr]

It should be up in 6.0.0-beta.1. Closing this one now, but if anything pops out, don't hesitate to reopen it again!