Change to batch dequeue.
Fixed synchronous ConnectableObservable.connect problem
GroubByUntil to use BufferUntilSubscriber
Add facilities for creating Observables from JavaFX events and ObservableValues.

Provides:
 * a Scheduler implementation ensuring execution in the JavaFX UI thread
 * a Subscription implementation ensuring that un-subscription happens in JavaFX UI thread
 * an Observable factory method for observing UI events on JavaFX nodes
 * an Observable factory method for observing value changes of a JavaFX ObservableValue

Also the rxjava-javafx is added to the gradle build.
Switch to direct accept and no instanceof
Merge pull request #1183 from akarnokd/NotificationLitePerf

NotificationLite.accept performance improvements
Merge pull request #1177 from akarnokd/GroupByUntilTimeGap

GroupByUntil to use BufferUntilSubscriber
Version 0.18.3
Merge pull request #1182 from amazari/rxjava-javafx

Merge pull request #1182
Add note to javadocs about ConnectableObservables requiring connect() call (#1180)
Fix issue #1187
Update the signature of "schedule" methods
Fix attempt #1
Negative schedule time now indicates immediate execution.
Fix issue #1196 and some docs issues
Comment explaining non-positive delay values
Adding marble diagrams to StringObservable operator javadocs
EDGE-1369 document runAsync/StoppableObservable
Might help with questions like in the email thread "javadoc for api-sdk in Eclipse: how to?"
Merge pull request #1188 from zsxwing/issue1187

Fix issue #1187 and #1196