Merge pull request ReactiveX#7 from abersnaze/undo_return_change

Change the return value back to an Observer because it was causing run time errors.

credentials

Release of 1.0.0

- Update README.md
- Merge pull request ReactiveX#2 from abersnaze/license
- added license to the source made the version concrete.
- Update README.md
- Update README.md

Release of 0.21.0