Rename test file, Class1 -> BlockMetadataTests
Make the block metadata offset a long

We can handle the memory hit I suspect.
Add very simple garbage collection of chunks.

Given a start position and a range, it clears out a square block
of chunks. Useful for unloading a region.
Add unloading support to Map

Adds various options for unloading chunks, broadly divided into two
categories: Expiration and Area and intersections between them.