v1.2.0

Below is a compilation of the changes from release candidates:

• Add Forwarder component (#187)
• Expose Prometheus metrics at /metrics endpoint (#168) - thanks @lebaptiste!
• Added extra TestConcurrentSubscribeMultipleTopics test (#196)
• Fixed docs (thanks @xswordsx and @sagikazarmark!)
• Accepting a prometheus.Registerer allows using prometheus.DefaultRegisterer (#204) - thanks @sagikazarmark!
• [bugfix] Proper Message nil m.ack handling (#227) - thanks @oxbambooxo
• [tests] Initialize subscribers for each consumer group (#225) - thanks @breml
• [examples] Add Server-Sent Events example (#209) - thanks @m110
• [docs] small docs updates - thanks @kochetkov-av and @m110
• [bugfix] Proper Message nil m.ack handling (#227) - thanks @oxbambooxo
• [tests] Initialize subscribers for each consumer group (#225) - thanks @breml
• [examples] Add Server-Sent Events example (#209) - thanks @m110
• [docs] small docs updates - thanks @kochetkov-av and @m110
• Add watermill-firestore to the list of Pub/Subs (#234) - thanks @boreq!
• Return the handler instance created within AddNoPublisherHandler (#229) - thanks @terev!
• Add mill googlecloud subscription ls (#220) - thanks @maclav3!
• Update deps and Go for CI
• Stress tests updates and bugfixes
• Documentation improvements #246, #252, #254, #255, #257 - thanks @boreq & @m110!
• Pass Context to Forwarder's wrapped message (#263) - thanks @m110!
• Implement FanIn component (#221) - thanks @0michalsokolowski0!
• Fix a blocking subscriber prevents other subscribers from receiving a message (#256) - thanks @boreq!
• Allowing to add handlers while the router is already running (#266)
• Added backward compatible build tags
• Add IsRunning method to the router (#270) - thanks @checkmunza!
• Changes to Pubsub Test for ExactlyOnce (#269) - thanks @AlexCuse!
• Add docs on publishing messages in transactions with help of the Forwarder component (#261) - thanks @czeslavo!
• Router handlers method for router plugins #289 - thanks @dangerousplay!
• update test setting (#329)