reduce memory by replacing object with struct. 
disable inspect, as it caused circular inspect bug when parent-child dual ref.
fix traversal check
state issue in comment
update uncommitted version file
Merge branch 'master' into reduce-memory
some refactoring and
fixed wrong custom prefixed column names on polymorphic association
added spec for :prefix option
bump version
Merge pull request #17 from alvinsj/reduce-memory

Reduce memory