Merge pull request #2 from NaturalNode/master

sync code to original
trim more than one space, can be used for ['','a','','c','',''], umm... maybe tokenizers only have one space, but this can do more things?
add longest path tree basic data structure and unit test for Chinese tokenizer.
fix 0.28+0.34=0.6200001 bug, add shortest path tree and unit tests, and also add SPT and LPT to index.js.
Add ngram and unit test for Chinese like launguages.
Add EdgeWeightedDigraph, and update usages of EdgeWeightedDigraph, ShortestPathTree, LongestPathTree in Readme.
ok, the digraph I draw can't display well in readme, delete it.
added ZH for chinese ngrams documentation