Added @objc for using this library with Objective-C projects

[prscX]

Hi,

First of all I would like to appreciate for creating such a cool library.

In order to use this library with Objective-C projects [e.g: ReactNative which is written in Objective-C]. I have add @objc for public API's.

Can you please merge the PR. Please let me know in case any changes are required.

Thanks </ Pranav >