initial commit
add new invertedindex
add the dblp test
1. complete the backward search
2. complete the import of dblp dataset
add the performancetracker and some test
complete the bidirection search algorithm. needs to supply the test code
1. complete the bidirection keyword search alogrithm. supply some simple
test.
2. refactor the organization of keywordsearch package
add unit test for BiSingleIterator
add the config component to dynamically determine the search algorithm
add the search algorithm factory
complete the graph interface for the keyword search.need to refactor the
modular of visualization.
external sort implementation