Merge pull request #3069 from ReactiveX/PLP

Improve toSingle() javadoc (diagram, see also, since-annotation)

Author: benjchristensen

src/main/java/rx/Observable.java

@@ -201,6 +201,7 @@ public interface Transformer<T, R> extends Func1<Observable<T>, Observable<R>> {
  * emits only a single item. If the source Observable emits more than one item or no items, notify of an
  * {@code IllegalArgumentException} or {@code NoSuchElementException} respectively.
  * <p>
+ * <img width="640" height="295" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/toSingle.png" alt="">
  * <dl>
  * <dt><b>Scheduler:</b></dt>
  * <dd>{@code toSingle} does not operate by default on a particular {@link Scheduler}.</dd>
@@ -211,6 +212,8 @@ public interface Transformer<T, R> extends Func1<Observable<T>, Observable<R>> {
  * if the source observable emits more than one item
  * @throws NoSuchElementException
  * if the source observable emits no items
+ * @see <a href="http://reactivex.io/documentation/single.html">ReactiveX documentation: Single</a>
+ * @since (if this graduates from Experimental/Beta to supported, replace this parenthetical with the release number)
  */
  @Experimental
  public Single<T> toSingle() {