* adding an upgraded event to conn
* set stopped flag asap
* trigger upgradded event on conn
* set concurrency limit for accepts
* backporting semaphore from tcp-limits2
* export unittests module
* make params explicit
* tone down debug logs
* adding semaphore tests
* use semaphore to throttle concurent upgrades
* add libp2p scope
* trigger upgraded event before any other events
* add event handler for connection upgrade
* cleanup upgraded event on conn close
* make upgrades slot release rebust
* dont forget to release slot on nil connection
* misc
* make sure semaphore is always released
* minor improvements and a nil check
* removing unneeded comment
* make upgradeMonitor a non-closure proc
* make sure the `upgraded` event is initialized
* handle exceptions in accepts when stopping
* don't leak exceptions when stopping accept loops
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