v2.0

• Various refactorings to split out large functions into more readable pieces
• Added a method to the Item interface to specify whether the item should be kept flat or not - this does not do anything yet, but adding now to avoid another major version bump later.

There are no bugfixes or packing logic changes in v2.0 compared to the latest v1.5 release - the bump in version number is purely because the interface has changed slightly.