This is a huge release, so please make sure to read it carefully.

Breaking Changes

• Remove flow (#3350) - you can read more about the reasoning behind it in the comments of the PR
• Remove NavigatorTypes (#3331) - thanks @brentvatne
• Reset state instead of pushing new routes for navigation actions in Drawer (#3164) - thanks @nico1510
• If you use Redux, please read https://reactnavigation.org/docs/redux-integration.html again!

New Features

• Navigation Event Subscriptions (#3345) - thanks @ericvicenti
• Add headerBackImage, closes #1999 - thanks @brentvatne
• Support initialRouteParams for TabRouters (#3352) - thanks @superburrito
• Add key support to StackRouter navigate (#3393) - thanks @ericvicenti
• Add Flow libdef (#3391) - thanks @Ashoat
• Redux middleware for new event system (#3399) - thanks @Ashoat

A set of new Stack actions, by @ericvicenti:

• StackRouter PopN Action (#3404)
• StackRouter PopToTop Action (#3403)
• New StackRouter Push Action (#3401)

Bugfixes & Improvements

• HeaderBackButton animation performance (#3305) - thanks @michaelduminy
• Simple fix to back button behavior (#3362) - thanks @ericvicenti
• Allow pure-wildcard route for nested navigators. (#2929) - thanks @moriyoshi
• Bring back TypeDefinition.js and re-add Flow to NavigationPlayground (#3363) - thanks @Ashoat
• Clean up when transitioner state when bailing out early - thanks @brentvatne
• Manually unset transitionIsRunning rather than going through _onTransitionEnd after state change - thanks @brentvatne
• Allow tabBarTestIDProps to be a function that receive the focused status (#3303) - thanks @iacopo87
• navigation back fix in example (#3218) - thanks @TheCodeTalker
• SafeAreaView style padding and inset collapse (#2917) - thanks @Freddy03h
• Don't forward back actions to inactive children of TabRouters (#2121) - thanks @monteithpj
• Add events support to redux example (#3368) - thanks @ericvicenti
• rely on defaultProps in TouchableItem (#3374) - thanks @vonovak
• Update to RN 0.52 and Expo 25 (#3383) - thanks @Ashoat
• Fix NavigationEvent types (#3384) - thanks @Ashoat
• Add NavigationPlayground Flow test to CI (#3385) - thanks @Ashoat
• metro-bundler -> metro (#3396) - thanks @Ashoat
• Fix and actually understand event emitter (#3367) - thanks @ericvicenti
• StackRouter Reset Action should match state key (#3400) - thanks @ericvicenti
• Clean up old build process and Babel config (#3406) - thanks @Ashoat

Documentation & Repo Chores

• Make examples use linked copy of react-navigation - thanks @skevy
• Update goBack docs (#2834) - thanks @tienf4m
• Fix the section link for Reset action (#3316) - thanks @pranavcode
• Update issue template & Add RFC and website repos to issue template - thanks @brentvatne
• Update repository URL in package.json (#3342) - thanks @greysteil
• Remove website deploy from CI and clean up scripts (#3353) - thanks @brentvatne
• Update TabNavigator.md (#3341) - thanks @dhruvdutt
• Update DrawerNavigator.md (#3337) - thanks @dhruvdutt
• Update Guide-Headers.md (#3335) - thanks @dhruvdutt

Please note that we are planning to move the documentation to its own repo; it's still a WIP, you can find it here.