added Observable.from_array for some examples
Make Observable#subscript to be acceptable 3 arguments like RxJS
Should sleep before calling block
Add library directories rx/linq and rx/linq/observable
Implement Observable#time_interval
Implement Observable.interval
Add Observable.timer
Fix to work Observable.timer

The context of t.exit is t, Thread.current == t, so the t.exit abort itself.
Add Observable.observable_timer_time_span
Merge pull request #32 from jca02266/implement-timer

Implement timer