implement urltable add/get with btree.
add the original parser from professor.
check whether met '<' before '>'.
implement generate posting from page data.
implement GetDataFileList ReadGZFile ParseIndex GetPages.
define the lexicon.
define the urltable.
add utility.
update gitignore and project file.
update invertedtable definition.
update main. just for test.
implment generate final inverted index and lexicon table.