Started working on circular references.
Initial version of the parent nodes functionality.
Unit test is fixed.
Circular references are fixed for collection parent.
Dictionary support for circular references is implemented.
Unit tests are fixed. Code clean-up is done.
Storing of the parent nodes information to index file storage is added.
Attribute to turn on the tracking of parent nodes for the reference is
added.
Minor implementation change.
Merge branch 'circular'
Merge branch 'master_old'