[RxScala] rxjava-scalaz: providing some type class instances.

Introduced 'rxjava-scalaz' project. This project provides some type class instances for Observable.

* _Monoid_: <br/>Observable obviously forms a monoid in terms of concatenation.
* _Functor, Applicative, Monad, MonadPlus_: <br/>Observable can be a Stream-like Monad and can be MonadPlus as well as Monoid.
* _Traverse, Foldable_: <br/>Observable can be Stream-like traversable.  Please note that the operations for the instance is blocking calls.
* etc.

About testing, property based tests are applied by Scalaz's ScalaCheck binding.
For getting started, please refer to rx.java.scala.scalaz.examples.RxScalazDemo, or README.md.

### Sample Usages
```scala
import scalaz._, Scalaz._
import rx.lang.scala.Observable
import rx.lang.scala.scalaz._

Observable.items(1, 2) |+| Observable.items(3, 4)               // === Observable.items(1 2 3 4)
Observable.items(1, 2) ∘ {_ + 1}                                // === Observable.items(2, 3)
(Observable.items(1, 2) |@| Observable.items(3, 4)) {_ + _}     // === Observable.items(4, 5, 5, 6)
1.η[Observable]                                                 // === Observable.items(1)
(Observable.items(3) >>= {(i: Int) => Observable.items(i + 1)}) // === Observable.items(4)
```

_My original proposal is #1167_