Remove unused dependency
Fix javadoc
Add eventDispatcher() to Transport

Transport belongs to a I/O thread, so users can access EventDispatcher
via Transport.
Change visibility of stage() to public
Remove unnecessary conversion
Remove adding offset_ to fromIndex

The indexOf() and lastIndexOf() checks from the current start index.
So the offset_ is not related.
Add method to check dispatcher change on proceed()
Copy buffer if the dispatcher is changed.
Add method to check a thread is dispatcher thread