Merge pull request #54 from younghz/master

Translate a part of 'Request and Response'
Merge pull request #55 from younghz/master

Translate 'Item Loaders'
Merge pull request #56 from younghz/master

Modify an error in 'settings.rst'
Merge branch 'master' of https://github.com/marchtea/scrapy_doc_chs