#5 suspend operation queue when pausing file item operations
#5 use vector and pair to chunk indices
#5 move TextMate's util functions to a util file
#5 chunk file item operations
#5 minor refactoring
#5 refactoring file item operation
#5 fix traversing when cached
#5 fix remove unnec' argument
#5 use operation queue for invalidating cache
#5 minor refactoring