Add javadoc comment to CollectionHelper.intersect().
Introduce CollectionHelper.difference() to identify different elements in two collections.
Extract delta comparison codes into private methods.
Rename CollectionHelper.difference() to CollectionHelper.delta().
Add class comment.
Add unit tests to test string inputs for CollectionHelper.delta().
Rename unit tests to distinguish integer-input tests from string-input tests.
Merge pull request #25 from ihcsim/collections-difference

Add Collections 'Delta' Method