Merge branch 'release/0.20.0-pre5' into development
Add temporary workaround for crashes related to ambiguous key paths in the deletion support. refs #1111
Fix logging issues with error method
Update Dynamic Mapping API's to match the rest of the 0.20.x style. Introduce support for predicate based dynamic matching.

* Rename RKDynamicMappingMatcher to RKObjectMappingMatcher since it is not strictly coupled to dynamic mapping and works with object mappings.
* Rework matchers into using a class cluster style to enable flexible subclassing to introduce additional matchers.
Implement Tarjan's algorithm to efficiently traverse the `RKResponseDescriptors` within the `RKManagedObjectRequestOperation` and compute the key paths to all managed objects. refs #1113, refs #1112
Rework implementation of managed object deletion and refetching to use the refreshed visitor implementation. refs #1111, #1113
Replace `[NSNull null]` in examples with nil to match current API
Add support and test for inversing a mapping containing attributes mapped with nil destination key paths. fixes #1116
Add test and fix for invalid key path exceptions with dynamic mappings. refs #1111
Fix issues with refetching results using visitation
Clean up the nasty mess in the visitor code and fix flaws in implementation of algorithm. Still some test breakage and additional coverage to put down
Restore cycle detection and cleanup visitor codebase further
Fix broken dynamic mapping test
Add support for skipping an aggregate relationship mapping in the event that the parent representation does not contain any values for the property mappings of the concrete `RKObjectMapping` configured for the relationship. fixes #1114, closes #1115
Drop instancetype from `init` methods since the compiler will infer it
Add support for deletion of mapped objects by predicate. closes #1109
Adjust completion block implementation for `RKPaginator` to enable completion block to be invoked when used without a strong reference. fixes #1119 fixes #1093
Fix issues with using the Paginator as documented in the headers. fixes #1117
Add support for deleting Core Data managed objects that fail validation out of the mapping context. This enables you to silently drop mapping for managed objects that fail validation. fixes #691 closes #694
Add support for customizing the HTTP request operation class used by `RKPaginator`. closes #1067