Add "error handling" java docs section to from callable & co (#6193)

* #6179 Adding Error handling javadocs to Observable#fromCallable(), Single#fromCallable(), and Completable#fromCallable().

* #6179 Adding Error handling javadocs to Maybe#fromAction() and Completable#fromAction().

* #6179 Removing cancellation language since only the `Flowable` type has `cancel()`

* #6179 Adding error handling JavaDocs to Flowable#fromCallable()

Author: luis-cortes

Diff for: src/main/java/io/reactivex/Completable.java

@@ -396,6 +396,13 @@ public static Completable error(final Throwable error) {
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code fromAction} does not operate by default on a particular {@link Scheduler}.</dd>
+     *  <dt><b>Error handling:</b></dt>
+     *  <dd> If the {@link Action} throws an exception, the respective {@link Throwable} is
+     *  delivered to the downstream via {@link CompletableObserver#onError(Throwable)},
+     *  except when the downstream has disposed this {@code Completable} source.
+     *  In this latter case, the {@code Throwable} is delivered to the global error handler via
+     *  {@link RxJavaPlugins#onError(Throwable)} as an {@link io.reactivex.exceptions.UndeliverableException UndeliverableException}.
+     *  </dd>
      * </dl>
      * @param run the runnable to run for each subscriber
      * @return the new Completable instance
@@ -416,6 +423,13 @@ public static Completable fromAction(final Action run) {
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code fromCallable} does not operate by default on a particular {@link Scheduler}.</dd>
+     *  <dt><b>Error handling:</b></dt>
+     *  <dd> If the {@link Callable} throws an exception, the respective {@link Throwable} is
+     *  delivered to the downstream via {@link CompletableObserver#onError(Throwable)},
+     *  except when the downstream has disposed this {@code Completable} source.
+     *  In this latter case, the {@code Throwable} is delivered to the global error handler via
+     *  {@link RxJavaPlugins#onError(Throwable)} as an {@link io.reactivex.exceptions.UndeliverableException UndeliverableException}.
+     *  </dd>
      * </dl>
      * @param callable the callable instance to execute for each subscriber
      * @return the new Completable instance

Diff for: src/main/java/io/reactivex/Flowable.java

@@ -1955,6 +1955,13 @@ public static <T> Flowable<T> fromArray(T... items) {
      *   <dd>The operator honors backpressure from downstream.</dd>
      *   <dt><b>Scheduler:</b></dt>
      *   <dd>{@code fromCallable} does not operate by default on a particular {@link Scheduler}.</dd>
+     *   <dt><b>Error handling:</b></dt>
+     *   <dd> If the {@link Callable} throws an exception, the respective {@link Throwable} is
+     *   delivered to the downstream via {@link Subscriber#onError(Throwable)},
+     *   except when the downstream has canceled this {@code Flowable} source.
+     *   In this latter case, the {@code Throwable} is delivered to the global error handler via
+     *   {@link RxJavaPlugins#onError(Throwable)} as an {@link io.reactivex.exceptions.UndeliverableException UndeliverableException}.
+     *   </dd>
      * </dl>
      *
      * @param supplier

Diff for: src/main/java/io/reactivex/Maybe.java

@@ -657,6 +657,13 @@ public static <T> Maybe<T> error(Callable<? extends Throwable> supplier) {
      * <dl>
      *  <dt><b>Scheduler:</b></dt>
      *  <dd>{@code fromAction} does not operate by default on a particular {@link Scheduler}.</dd>
+     *  <dt><b>Error handling:</b></dt>
+     *  <dd> If the {@link Action} throws an exception, the respective {@link Throwable} is
+     *  delivered to the downstream via {@link MaybeObserver#onError(Throwable)},
+     *  except when the downstream has disposed this {@code Maybe} source.
+     *  In this latter case, the {@code Throwable} is delivered to the global error handler via
+     *  {@link RxJavaPlugins#onError(Throwable)} as an {@link io.reactivex.exceptions.UndeliverableException UndeliverableException}.
+     *  </dd>
      * </dl>
      * @param <T> the target type
      * @param run the runnable to run for each subscriber

Diff for: src/main/java/io/reactivex/Observable.java

@@ -1757,8 +1757,14 @@ public static <T> Observable<T> fromArray(T... items) {
      * <dl>
      *   <dt><b>Scheduler:</b></dt>
      *   <dd>{@code fromCallable} does not operate by default on a particular {@link Scheduler}.</dd>
+     *   <dt><b>Error handling:</b></dt>
+     *   <dd> If the {@link Callable} throws an exception, the respective {@link Throwable} is
+     *   delivered to the downstream via {@link Observer#onError(Throwable)},
+     *   except when the downstream has disposed this {@code Observable} source.
+     *   In this latter case, the {@code Throwable} is delivered to the global error handler via
+     *   {@link RxJavaPlugins#onError(Throwable)} as an {@link io.reactivex.exceptions.UndeliverableException UndeliverableException}.
+     *   </dd>
      * </dl>
-     *
      * @param supplier
      *         a function, the execution of which should be deferred; {@code fromCallable} will invoke this
      *         function only when an observer subscribes to the ObservableSource that {@code fromCallable} returns

Diff for: src/main/java/io/reactivex/Single.java

@@ -583,6 +583,13 @@ public static <T> Single<T> error(final Throwable exception) {
      * <dl>
      *   <dt><b>Scheduler:</b></dt>
      *   <dd>{@code fromCallable} does not operate by default on a particular {@link Scheduler}.</dd>
+     *   <dt><b>Error handling:</b></dt>
+     *   <dd> If the {@link Callable} throws an exception, the respective {@link Throwable} is
+     *   delivered to the downstream via {@link SingleObserver#onError(Throwable)},
+     *   except when the downstream has disposed this {@code Single} source.
+     *   In this latter case, the {@code Throwable} is delivered to the global error handler via
+     *   {@link RxJavaPlugins#onError(Throwable)} as an {@link io.reactivex.exceptions.UndeliverableException UndeliverableException}.
+     *   </dd>
      * </dl>
      *
      * @param callable