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#agregate
Should pass the proc object for Scheduler#schedule_recursive
Fix to work Observable#start_with(1)
Re-fix Observable.zip to be acceptable result_selector block
Add Observable.observable_timer_time_span
Merge pull request #34 from jca02266/fix-zip

Fix Observable.zip to accept a block
Merge pull request #32 from jca02266/implement-timer

Implement timer
Merge pull request #33 from jca02266/implement-aggregate

Implement aggregate
Correct combine_latest same as RxJS's one
Change the Subscriptn to base module
Observable.create block may return Proc object
Add alias RX::Disposable for RX::Subscription
Add dispose method, alias of unsubscribe