https://developer.apple.com/library/downloads/docset-index.dvtdownloadableindex
https://devimages.apple.com.edgekey.net/docsets/20150309/Xcode_6.2_DevTools_Docset.dmg xcode6.2文档
https://devimages.apple.com.edgekey.net/docsets/20150408/Xcode_6.3_DevTools_Docset.dmg xcode6.3文档
https://devimages.apple.com.edgekey.net/docsets/20150309/Xcode_6.2_OS_X_Docset.dmg OS X 10.10
https://devimages.apple.com.edgekey.net/docsets/20150309/Xcode_6.2_iOS_Docset.dmg ios 8.2