* Create new method 'parse', 'parse_children', 'parse_element'
* Add test data for using rspec
* Add new gem 'ActiveSupport'
   * For using Hash#from_xml method
* modify sample xml
   * strip any long descriptions
* Add new sample data of "i.nicovideo.jp" endpoint response
   * It is different from "ext.nicovideo.jp" endpoint response
* Write new spec for using new a sample002.xml
* make test "in tags", "in thread"
* change " → '
* remove 'nokogiri'
   * it is unnecessary
* create 'response' class
   * touch files