Modified the Objective-C implementation to use ARC

[stevenklassen8376]

This change does three things:

1. Updates the Xcode project to support the latest Xcode (11.5),
2. Make the Apple recommended settings to the Xcode project, and
3. (most importantly) Updates the project and the code to use
   Automatic Reference Counting (ARC).

Closes #97

[stevenklassen8376]

I'm closing this pull request as the Objective-C code just seems to be too old to work well with Swift. Instead I have created a Swift port of the Python3 version of the code. Unfortunately there does not seem to be a simple way to work with a Swift package that is a subset of a git repository, so I've created the Swift port as my own project at https://github.com/klassen-software-solutions/KSSDiff. If requested I could copy the code into a swift subdirectory of this project, but I don't really see any point of that.

[JanX2]

@stevenklassen8376
This may have been what you were looking for. Though it’s not well maintained either.

[stevenklassen8376]

I decided to go a different route and create a native Swift implementation by porting the Python3 version (since it was easy to read and understand).