Polishing.

Tweak Javadoc. Add since tag, reformat code. Simplify tests. Move documentation bits into the right place.

See #3726.
Original pull request: #3765.

src/main/asciidoc/reference/mongo-repositories.adoc

@@ -281,10 +281,6 @@ lower / upper bounds (`$gt` / `$gte` & `$lt` / `$lte`) according to `Range`
 | `Exists`
 | `findByLocationExists(boolean exists)`
 | `{"location" : {"$exists" : exists }}`
-
-| `SampleRate`
-| `sampleRate(double sampleRate)`
-| `{"$sampleRate" : sampleRate }`
 |===
 
 NOTE: If the property criterion compares a document, the order of the fields and exact equality in the document matters.

src/main/asciidoc/reference/mongodb.adoc

@@ -1219,6 +1219,7 @@ The `Criteria` class provides the following methods, all of which correspond to
 * `Criteria` *orOperator* `(Criteria... criteria)` Creates an or query using the `$or` operator for all of the provided  criteria
 * `Criteria` *orOperator* `(Collection<Criteria> criteria)` Creates an or query using the `$or` operator for all of the provided  criteria
 * `Criteria` *regex* `(String re)` Creates a criterion using a `$regex`
+* `Criteria` *sampleRate* `(double sampleRate)` Creates a criterion using the `$sampleRate` operator
 * `Criteria` *size* `(int s)` Creates a criterion using the `$size` operator
 * `Criteria` *type* `(int t)` Creates a criterion using the `$type` operator
 * `Criteria` *matchingDocumentStructure* `(MongoJsonSchema schema)` Creates a criterion using the `$jsonSchema` operator for <<mongo.jsonSchema,JSON schema criteria>>. `$jsonSchema` can only be applied on the top level of a query and not property specific. Use the `properties` attribute of the schema to match against nested fields.