DATAMONGO-1824 - Polishing.

Introduce Aggregation.toPipeline(…) method to render the aggregation pipeline directly. Adapt code using aggregation pipelines. Consider allowDiskUse and batchSize cursor options. Move introduction versions to 2.1. Mention migration to cursor-based aggregation in reference docs.

Original pull request: #515.

src/main/asciidoc/new-features.adoc

@@ -1,6 +1,10 @@
 [[new-features]]
 = New & Noteworthy
 
+[[new-features.2-1-0]]
+== What's new in Spring Data MongoDB 2.1
+* Cursor-based aggregation execution.
+
 [[new-features.2-0-0]]
 == What's new in Spring Data MongoDB 2.0
 * Upgrade to Java 8.

src/main/asciidoc/reference/mongodb.adoc

@@ -1410,7 +1410,7 @@ List<Person> results = template.find(query, Person.class);
 ----
 Collation collation = Collation.of("de");
 
-AggregationOptions options = new AggregationOptions.Builder().collation(collation).build();
+AggregationOptions options = AggregationOptions.builder().collation(collation).build();
 
 Aggregation aggregation = newAggregation(
   project("tags"),