Implemented the "isValidObject:" public method on RCObject.
Improved the "dateFromString:" method on RCObject to support the "yyyy-MM-dd HH:mm:ss" date format.
Fixed the NULL validity on every RCObject class by calling the "isValidObject:" method.
Updated the version number inside the files and the pod spec to 0.7.1.
Updated the current project version to 0.7.1.
Updated the CHANGES document with the changes for the version 0.7.1.