Added error handling when JSON results are empty

• #200: Now logs out an error if the App Store JSON results are empty. This will only get thrown if the countryCode variable was not set and you're available in the US App Store (e.g., the default store). Thanks to @vinczebalazs for pointing out that this code path was not covered.

Added ability to override default messages

#187: Adds the SirenAlertMessaging struct, which allows for custom overriding of messaging in UIAlertController update modal.

        siren.alertMessaging = SirenAlertMessaging(updateTitle: "New Fancy Title",
                                                   updateMessage: "New message goes here!",
                                                   updateButtonMessage: "Update Now, Plz!?",
                                                   nextTimeButtonMessage: "OK, next time it is!",
                                                   skipVersionButtonMessage: "Please don't push skip, please don't!")

Updates to Arabic and Dutch Languages

• #182: Updated Arabic language Localization - thanks @AttiaMo
• #185 (Harpy): Updated Dutch Language Localization - thanks @wbison

Add Missing Imports for Static Library Compilation

• #179
  • Adds missing import UIKit in a couple files so the library can be built as a Static Library (thanks to @NSemakov)

Removed Deprecated Code

• #176
  • The Xcode 9.1 betas throw warnings/errors around the characters API.
  • @VladislavJevremovic kindly reminded me of this issue and put together a small PR to remove all instances of characters.
  • These changes are backwards compatible to iOS 8 as long as you're building with Xcode 9.

Added Ukrainian Localization

• #175: Adds Ukrainian Localization (thanks to @dimacheverda)

Fixed Transitive Dependency Issue

There were private/fileprivate scoping issues if Siren was installed as a transitive dependency (e.g., as a dependency in a pod's podspec, which then was a dependency of an app's podfile).

This has been addressed.

SirenError is now Public

• Fixes #174: SirenError is now public, allow for sirenDidFailVersionCheck(:) to be called properly.

Re-enalbed isUpdateCompatibleWithDeviceOS check

#173: Re-enabled the isUpdateCompatibleWithDeviceOS, which may have become disabled when converting (and massively refactoring) the codebase from Swift 3.1 to Swift 4.

Expanded sirenDidDetectNewVersionWithoutAlert method

Issue #168 & PR #171 (Thanks to @JussiSuojanen)

• The sirenDidDetectNewVersionWithoutAlert(message:) type is now sirenDidDetectNewVersionWithoutAlert(message:updateType:). The updateType parameter represents the type of update (major, minor, patch, revision).

Due to issues with how @availabile(*unavailable) works in protocols, the original method was removed, instead of deprecated.