In-flight request limiting

[reivilibre]

Intended to provide a general increase in robustness/fault-tolerance, e.g. to address #117 .

[richvdh]

looks good.

A word of advice: beware of overusing inheritance. It feels whizzy, but it's easy to end up with code that's hard to follow. in this case it might have been better to have a ConcurrencyLimiter object, where you can go:

async def dispatch_notification(self, n, device, context):
    with concurrency_limiter.limit():
        return await self._dispatch_notification_unlimited(n, device, context)

but I think this is fine.

[reivilibre]

Thanks, I'll bear it in mind :)