Merge branch 'release/v0.20.0-rc1'
Merge branch 'release/0.20.0'
Drop pre from README.md install instructions
Merge branch 'release/0.20.1'
Adjust version and tag in Podspec for release
Merge branch 'release/0.20.2'
Merge branch 'release/0.20.3'
adding new ObjectManager methods for building RKObjectRequestOperation objects that take an array of response descriptors.  Updated appropriateObjectRequestOperationWithObject:method:path:parameters: to pass only the response descriptors that match the object, path, and method passed in.
changed Error code when response mapping declined with `willMapDeserializedResponseBlock` block
Migrate RKValueTransformers and ISO8601DateFormatter into standalone libraries
Remove warning log message that is likely to produce log flooding
Fix issue with inappropriate handling of managed objects using `nil` key path. fixes #1596
Switch `RKValueTransformers` and `ISO8601DateFormatterValueTransformer` to HTTP submodule URL's
Fix memory leak in state machine. closes #1593
Fix documentation issue on `addAttributeMappingToKeyOfRepresentationFromAttribute:` and transparently transition to using braces instead of parentheses for denoting variables in key paths. closes #1449
Merge pull request #1570 from almassapargali/development

changed Error code when response mapping declined with `willMapDeserializedResponseBlock` block
Rename and deprecate some poorly named properties on `RKObjectMapping`
Bump VERSION to 0.21.0
Update RestKit to build and run tests using CocoaPods instead of the static library / framework targets
Integrate tests verifying the behavior of using an externally integrated value transformer for mapping and object parameterization