Missing documentation on Delta

The documentation on [`DeltaType`](https://github.com/java-diff-utils/java-diff-utils/blob/master/java-diff-utils/src/main/java/com/github/difflib/patch/DeltaType.java#L22) is not helpful. What do they actually mean?

I would suggest adding `patch`-files and test cases that shows how these `patch`-files triggers each `DeltaType`.