DATACMNS-937 - Document JavaSlang's Option type as query method return type.

Mentioned the support for Scala's Option type, too.

Author: odrotbohm

Diff for: src/main/asciidoc/repository-query-return-types-reference.adoc

@@ -19,6 +19,7 @@ NOTE: Geospatial types like (`GeoResult`, `GeoResults`, `GeoPage`) are only avai
 |`Collection<T>`|A `Collection`.
 |`List<T>`|A `List`.
 |`Optional<T>`|A Java 8 or Guava `Optional`. Expects the query method to return one result at most. In case no result is found `Optional.empty()`/`Optional.absent()` is returned. More than one result will trigger an `IncorrectResultSizeDataAccessException`.
+|`Option<T>`|An either Scala or JavaSlang `Option` type. Semantically same behavior as Java 8's `Optional` described above.
 |`Stream<T>`|A Java 8 `Stream`.
 |`Future<T>`|A `Future`. Expects method to be annotated with `@Async` and requires Spring's asynchronous method execution capability enabled.
 |`CompletableFuture<T>`|A Java 8 `CompletableFuture`. Expects method to be annotated with `@Async` and requires Spring's asynchronous method execution capability enabled.