Ensure that calling cancel() deallocates the subscription

Avoid last request after cancellation (#10)

Fix retain cycle (#9)

* Fix retain cycle

STR:
- have an app with a few long polls
- put the app in background
- wait a minute (t > long poll timeout)
- resume the app

Result:
- 💣 memory allocation skyrockets

* Move the dispacht-async call to the call site, get rid of some selfs in startPolling()

Fix retain cycle (#9)

* Fix retain cycle

STR:
- have an app with a few long polls
- put the app in background
- wait a minute (t > long poll timeout)
- resume the app

Result:
- 💣 memory allocation skyrockets

* Move the dispacht-async call to the call site, get rid of some selfs in startPolling()

Make mock conform to the protocol it's mocking (#8)

Remove RESTClient dependency (#7)

Enforce long polling session to have timeout vars too (#6)

Invert dependency (#5)

Fix "Semaphore object deallocated while in use"-crash 🤞 (#4)

* Fix "Semaphore object deallocated while in use"-crash 🤞

* Fix the initial value as well

(this has no practical impact, I just want to avoid having DispatchSemaphore(value:1) anywhere in the code)

Fix the missing lock in the longpoll loop (#3)