Implemented 'cast' operator

Author: zsxwing

rxjava-core/src/main/java/rx/Observable.java

@@ -4332,6 +4332,23 @@ public BlockingObservable<T> toBlockingObservable() {
         return BlockingObservable.from(this);
     }
 
+    /**
+     * Converts the elements of an observable sequence to the specified type.
+     *
+     * @return An observable sequence that contains each element of the source
+     *         sequence converted to the specified type.
+     *
+     * @see <a href="http://msdn.microsoft.com/en-us/library/hh211842(v=vs.103).aspx">MSDN: Observable.Cast</a>
+     */
+    public <R> Observable<R> cast() {
+        return map(new Func1<T, R>() {
+            @SuppressWarnings("unchecked")
+            public R call(T t) {
+                return (R) t;
+            }
+        });
+    }
+
     /**
      * Whether a given {@link Function} is an internal implementation inside rx.* packages or not.
      * <p>