BREAKING CHANGE: Update API for connection, communication channel state and is browser value (#14)

* refactor(lib, example, example_full): use streams for communication channel and is ios browser

* feat: add abstract toJson() to message

* refactor: add deprecations for nearby_service

* feat(example): update main.dart

* feat(nearby_service): add comments

* feat(nearby_service_platform_interface): add deprecation to getConnectedDeviceStream

* feat(nearby_service/message): add concrete implementation for toJson()

* feat(nearby_service/android): add deprecations

* fix(nearby_service/android): reset check for android device

* fix(nearby_service/ios): change ios service to deprecations variant

* chore(nearby_service): edit deprecation messages

* chore: update gitignore

* doc: add CONTRIBUTING file

* doc: update CONTRIBUTING file

* chore: update CONTRIBUTING.md

* chore: update CONTRIBUTING.md

* chore: version 0.1.0

* fix(example_full): move startListeningCommunicationChannelState() upper

test/nearby_service_test.dart

@@ -49,6 +49,12 @@ class MockNearbyServicePlatform
     throw UnimplementedError();
   }
 
+  @override
+  Stream<NearbyDevice?> getConnectedDeviceStreamById(String deviceId) {
+    // TODO: implement getConnectedDeviceStreamById
+    throw UnimplementedError();
+  }
+
   @override
   Future<NearbyDeviceInfo?> getCurrentDeviceInfo() {
     // TODO: implement getCurrentDevice