SWORD25: Move all lua serialization helper functions to their own file
SWORD25: Update module.mk with lua serialization changes
SWORD25: Use new lua serialization functions to persist state
SWORD25: Rename lua serialization functions to use 'persist' in order to match the rest of the engine
SWORD25: Rename double serialization file to better represent what it is

AKA functions, rather than a class
SWORD25: Fix how nils are persisted

The unpersist code expects nils to be represented as an index with value 0.
The persist code incorrectly wrote out this data
SWORD25: Remove old lua persistence files