Update to swift4

Update README.md

Update task class and support class for more convenience and remove success,failure function from task class due to api design guideline.

Update README.md

Update README.md

Remove redundancy variable in Query.swift

Update podspec

Modify access level in Query.swift

Update podspec

Update swift version to 3.0

Update to swift3 syntax

Update podfile and install

Update podspec

Change swift version to 3.0

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