addsd shortcut methods
new Timer class
move unit tests to correct package
PromiseImpl: add String representation & ignore `set' when done
Worker: provide a default `cast' method
Future: add `pipeTo' and `within' operations
Future: add an alias to `bind' as `flatMap'
Future: add shortcut methods `onSuccess' and `onFailure'
Future: simplifies ConstFuture#bind