update sample and documentation to iOS SDK 4.11.

update podspec file.

update sample to iOS SDK 4.9.1.

update Sample Code and Documentation to iOS SDK 4.9.

Merge branch 'master' of github.com:dji-sdk/Mobile-SDK-iOS

update sample to iOS SDK 4.8.1.

update Sample Code and Documentation to iOS SDK 4.8.

update sample to iOS SDK 4.7.1.

update sample and doc to iOS SDK 4.7.

update sample to iOS SDK 4.6.1.