[zh] follow changes from en
[zh_CN] rename zh to zh_CN for Simplified Chinese, leaving zh_TW for Traditional Chinese (ref: http://sphinx-doc.org/config.html#confval-language)
[zh] fix sphinx build warning
Merge branch 'zh' into zh-work

Conflicts:
	config/all.py
	zh/contents.rst
	zh/epub-contents.rst
[zh_CN] rename zh to zh_CN for Simplified Chinese, leaving zh_TW for Traditional Chinese (ref: http://sphinx-doc.org/config.html#confval-language)