Migration to Swift 4.2

[altagir]

Pull requests

The easiest way to start contributing is searching open issues by help wanted tag.

• Add test coverage to the feature or fix if you can. We are more likely to accept new feature pull requests that have related test coverage. This allows us to keep the library stable as we move forward.
• Remember to document the new feature. We do not accept new feature pull requests without its associated documentation.
• In case of a new feature please update the example project showing the feature.
• Please only one fix or feature per pull request. This will increase the chances your feature will be merged.

[pavankataria]

There's a few conflicts here, but don't worry I'll merge this in.