DATAMONGO-1005 - Improve cycle-detection for DbRef's.

Introduced ObjectPath that collects the target objects while converting a DBObject to a domain object. If we detect that a potentially nested DBRef points to an object that is already under construction we simply return a reference to that object in order to avoid StackOverFlowErrors.

Original pull request: #209.
DATAMONGO-1005 - Polishing introduction of ObjectPath.

Simplified implementation of ObjectPath to use a static root instance and hand the path further down until final resolution in MappingMongoConverter.readValue(…). This removes a bit of boxing and unboxing code both in ObjectPath and the converter.

Introduced ObjectPath.getPathItem(…) to internalize the iteration to find a potentially already resolved object.

Renamed parameters and fields of type ObjectPath to path consistently. Removed obsolete method in MappingMongoConverter.

Original pull request: #209.
DATAMONGO-1020 - LimitOperation is now a public class.

Original pull request: #218.
DATAMONGO-957 - Add support for query modifiers.

Prepare issue branch.
DATAMONGO-957 - Add support for query modifiers.

Using Meta allows to the define $comment, $maxScan, $maxTimeMS and $snapshot on query. When executed we add the meta information to the cursor in use.

We’ve introduced the @Meta annotation that allows to the define $comment, $maxScan, $maxTimeMS and $snapshot on a repository finder method.