Update amb.md

Fixed missing a comma in Promises example
Fix typo
Fix signature of Observable.start/toAsync on documents.
Fix to match the output
Correct the example of Observable.using
Merge pull request #465 from jca02266/fix-examples

Fix examples in observable.md
Merge pull request #464 from YuvalZiegler/patch-1

Update amb.md
Replace then to thenDo
Merge pull request #466 from jca02266/fix-examples

Replace then to thenDo
Fixing Issue #457
Fixing Issue #453
Closing Issue #433
Fixing Issue #431
Fixing Issue #423
Fix typo