Simplify get_chunk_data(); remove region/chunk save functions

Now that we have an option for limits, the save functions on the region
and chunk levels are a little unnecessary.
World and image constructors now return pointers

- World and image structs are now allocated on the heap
- Did some renaming so types and variables of above are named
differently
- Free functions for the above now have to free the whole struct as well
Remove redundant tiny world map functions