# Functions
NewIdf create a new Idf.
NewStopWord create a new StopWord with the default stop words.
# Variables
StopWordMap the default stop words.
# Structs
Idf type a dictionary for all words with the IDFs(Inverse Document Frequency).
StopWord is a dictionary for all stop words.
TagExtracter is extract tags struct.
TextRanker is extract tags struct.